NETRESEC Network Security Blog


Discovered Artifacts in Decrypted HTTPS

We released a PCAP file earlier this year, which was recorded as part of a live TLS decryption demo at the CS3Sthlm conference. The demo setup used PolarProxy running on a Raspberry Pi in order to decrypt all HTTPS traffic and save it in a PCAP file as unencrypted HTTP.

Laptop, Raspberry Pi, PolarProxy, Internet ASCII

This capture file was later used as a challenge for our twitter followers, when we made the following announcement:

PCAP CHALLENGE!
The capture file released in this blog post contains a few interesting things that were captured unintentionally. Can you find anything strange, funny or unexpected in the pcap file? (1/2)

Followed by this message:

The person to submit the most interesting answer wins a “PCAP or it didn’t happen” t-shirt. Compete by including your discovery in a retweet or reply to this tweet, or in an email to info(at)netresec.com. We want your answers before the end of January. (2/2)

We'd like to thank everyone who submitted answers in this challenge, such as David Ledbetter, Christoffer Strömblad, RunΞ and Chris Sistrunk.

We're happy to announce that the winner of our challenge is David Ledbetter. Congratulations David!

So what were the interesting thing that could be found in the released capture file? Below is a short summary of some things that can be found.

Telemetry data sent to mozilla.org

A surprising amount of information about the Firefox browser was sent to incoming.telemetry.mozilla.org, including things like:

  • Active browser addons
  • Active browser plugins
  • Firefox profile creation date
  • Browser search region
  • Default search engine
  • Regional locales
  • Screen width
  • Screen height
  • CPU vendor, family and model
  • HDD model, revision and type
  • Installed RAM
  • Operating system
  • Etc..

Here's an excerpt showing a part of the data sent to Mozilla:

"build": { "applicationId": "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}", "applicationName": "Firefox", "architecture": "x86-64", "buildId": "20191002194346", "version": "69.0.2", "vendor": "Mozilla", "displayVersion": "69.0.2", "platformVersion": "69.0.2", "xpcomAbi": "x86_64-gcc3", "updaterAvailable": false }, "partner": { "distributionId": "canonical", "distributionVersion": "1.0", "partnerId": "ubuntu", "distributor": "canonical", "distributorChannel": "ubuntu", "partnerNames": [ "ubuntu" ] }, "system": { "memoryMB": 3943, "virtualMaxMB": null, "cpu": { "count": 1, "cores": 1, "vendor": "GenuineIntel", "family": 6, "model": 42, "stepping": 7, "l2cacheKB": 256, "l3cacheKB": 4096, "speedMHz": null, "extensions": [ "hasMMX", "hasSSE", "hasSSE2", "hasSSE3", "hasSSSE3", "hasSSE4_1", "hasSSE4_2", "hasAVX", "hasAES" ] }, "os": { "name": "Linux", "version": "5.0.0-31-generic", "locale": "en-US" }, "hdd": { "profile": { "model": null, "revision": null, "type": null }, "binary": { "model": null, "revision": null, "type": null }, "system": { "model": null, "revision": null, "type": null } }, "gfx": { "D2DEnabled": null, "DWriteEnabled": null, "ContentBackend": "Skia", "Headless": false, "adapters": [ { "description": "llvmpipe (LLVM 8.0, 256 bits)", "vendorID": "0xffff", "deviceID": "0xffff", "subsysID": null, "RAM": 3942, "driver": null, "driverVendor": "mesa/llvmpipe", "driverVersion": "19.0.8.0", "driverDate": null, "GPUActive": true } ], "monitors": [ { "screenWidth": 681, "screenHeight": 654 } ], "features": { "compositor": "basic", "gpuProcess": { "status": "unavailable" }, "wrQualified": { "status": "blocked-vendor-unsupported" }, "webrender": { "status": "opt-in" } } }, "appleModelId": null }, "settings": { "blocklistEnabled": true, "e10sEnabled": true, "e10sMultiProcesses": 8, "telemetryEnabled": false, "locale": "en-US", "intl": { "requestedLocales": [ "en-US" ], "availableLocales": [ "en-US", "en-CA", "en-GB" ], "appLocales": [ "en-US", "en-CA", "en-GB", "und" ], "systemLocales": [ "en-US" ], "regionalPrefsLocales": [ "sv-SE" ], "acceptLanguages": [ "en-US", "en" ] }, "update": { "channel": "release", "enabled": true, "autoDownload": false }, "userPrefs": { "browser.cache.disk.capacity": 1048576, "browser.search.region": "SE", "browser.search.widget.inNavBar": false, "network.trr.mode": 2 }, "sandbox": { "effectiveContentProcessLevel": 4 }, "addonCompatibilityCheckEnabled": true, "isDefaultBrowser": false, "defaultSearchEngine": "google", "defaultSearchEngineData": { "name": "Google", "loadPath": "[distribution]/searchplugins/locale/en-US/google.xml", "origin": "default", "submissionURL": "https://www.google.com/search?client=ubuntu&channel=fs&q=&ie=utf-8&oe=utf-8" } }, "profile": { "creationDate": 18183, "firstUseDate": 18183 }

You can use the following Wireshark display filter to find all the data sent to Mozilla:

http.request.method eq POST and http.host contains telemetry

Public IP Revealed in PCAP

The client's IP address was 192.168.4.20, which is part of the RFC 1918 192.168/16 private address space. It's therefore safe to assume that the client was behind a NAT (the client was in fact behind a double NAT). However, we noticed that the public IP of the client was revealed through multiple services in the captured network traffic. One of these services is the advertising exchange company AppNexus (adnxs.com), which sent the client's public IP address 193.235.19.252 in an X-Proxy-Origin HTTP header.

X-Proxy-Origin HTTP header in Wireshark

You can use the following Wireshark/tshark display filter to find X-Proxy-Origin headers:

http.response.line matches "x-proxy-origin" or http2.header.name matches "x-proxy-origin"

We are using the "matches" operator here instead of "contains" or "==" because we want to perform case insensitive matching. You might also notice that we need a completely different display filter syntax to match HTTP/2 headers compared to what we are used to with HTTP/1.1.

Monty Python "Majestik møøse" reference in reddit x-header

The reddit server 151.101.85.140 sends an HTTP/2 header called "x-moose" with a value of "majestic".

x-moose 1 : majestic header from reddit

This header refers to the opening credits of Monty Python and the Holy Grail.

Wi nøt trei a høliday in Sweden this yër?

Posted by Erik Hjelmvik on Tuesday, 17 March 2020 09:00:00 (UTC/GMT)

Tags: #HTTP/2 #http2 #TLS #decrypt #TLSI #PolarProxy #NetworkMiner #Wireshark #CS3Sthlm #CS3 #Forensics #PCAP

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Reverse Proxy and TLS Termination

PolarProxy is primarily a TLS forward proxy, but it can also be used as a TLS termination proxy or reverse TLS proxy to intercept and decrypt incoming TLS traffic, such as HTTPS or IMAPS, before it is forwarded to a server. The proxied traffic can be accessed in decrypted form as a PCAP formatted data stream, which allows real-time analysis of the decrypted traffic by an IDS as well as post incident forensics with Wireshark.

PolarProxy version 0.8.15 and later can import an existing X.509 server certificate (aka leaf certificate or end-entity certificate) in order to perform the TLS decryption using a valid certificate signed by a trusted certificate authority. If no server certificate is provided, then PolarProxy falls back to generating server certificates on the fly and signing them with its own root CA certificate.

There are two principal ways to run PolarProxy as a reverse proxy, either as a TLS termination proxy or as a reverse proxy that decrypts and re-encrypts the traffic.

PolarProxy as a TLS Termination Proxy

TLS Termination Proxy

The TLS termination proxy mode is useful in order to offload the task of performing TLS encryption to PolarProxy instead of doing the decryption on the web server. This mode can also be used when the proxied services don’t support TLS encryption, such as legacy web servers or servers hosting other unencrypted services that you want to secure with TLS.

The following command sequence shows how to create a Let’s Encrypt SSL certificate, convert it to the PKCS#12 format, and load the server certificate into PolarProxy to terminate incoming HTTPS connections. In this setup PolarProxy decrypts the TLS traffic and relays the HTTP traffic to the web server on TCP port 80.

sudo certbot certonly --manual --preferred-challenges dns -d example.com,www.example.com

sudo openssl pkcs12 -export -out /etc/example.p12 -inkey /etc/letsencrypt/live/example.com/privkey.pem -in /etc/letsencrypt/live/example.com/fullchain.pem --passout pass:PASSWORD

sudo mkdir /var/log/TlsTerminationProxy/

sudo ./PolarProxy --terminate --connect 10.1.2.3 --nosni www.example.com --servercert example.com,www.example.com:/etc/example.p12:PASSWORD -p 443,80,80 -o /var/log/TlsTerminationProxy/

Here’s a breakdown of the arguments sent to PolarProxy:

  • --terminate : Terminate incoming TLS sessions and forward proxied traffic in unencrypted form.
  • --connect 10.1.2.3 : Forward all proxied traffic to 10.1.2.3 instead of connecting to the host name provided in the SNI extension of the TLS ClientHello message.
  • --nosni www.example.com : Treat incoming TLS sessions that don’t define a host name with the SNI extension as if they wanna to connect to “www.example.com”.
  • --servercert example.com,www.example.com:/etc/example.p12:PASSWORD : Use the server certificate “/etc/example.p12” for incoming connections to “example.com” and “www.example.com”.
  • -p 443,80,80 : Listen on TCP port 443, save decrypted traffic in PCAP file as if it was directed to port 80, forward decrypted traffic to port 80.
  • -o /var/log/TlsTerminationProxy/ : Save decrypted traffic to hourly rotated PCAP files in “/var/log/TlsTerminationProxy/”.

PolarProxy is a generic TLS proxy that doesn’t care what application layer protocol the TLS tunnel carries. So if you want to terminate the TLS encryption of incoming IMAPS sessions as well, then simply append an additional argument saying “-p 993,143,143” to also forward decrypted IMAP sessions to 10.1.2.3. This method can be used in order to wrap almost any TCP based protocol in a TLS tunnel, which can be useful for privacy reasons as well as to prevent network monitoring tools from detecting the actual application layer protocol.

PolarProxy as a Reverse TLS Proxy

Reverse TLS Proxy

There are setups for which it is preferable to also encrypt the internal sessions between PolarProxy and the final server. One such setup is when the server is hosting a web service with support for the HTTP/2 protocol, which in practice always uses TLS. Luckily PolarProxy is designed to decrypt and re-encrypt proxied traffic while also forwarding important TLS parameters, such as ALPN and SNI, between the internal and external TLS sessions.

To use TLS encryption on the inside as well as outside of PolarProxy, simply do as explained in the previous TLS termination section, but remove the “--terminate” argument and change the port argument to “-p 443,80,443” like this:

sudo ./PolarProxy --connect 10.1.2.3 --nosni www.example.com --servercert example.com,www.example.com:/etc/example.p12:PASSWORD -p 443,80,443 -o /var/log/ReverseTlsProxy/

PolarProxy will save the decrypted traffic as cleartext HTTP (or HTTP/2) to PCAP files in the “/var/log/ReverseTlsProxy/” directory.

Real-Time Analysis of Decrypted Traffic

Both the external (client-to-proxy) and internal (proxy-to-server) TCP sessions, in the reverse TLS proxy example above, are encrypted with TLS. This prevents passive network security monitoring tools, such as IDSs, DPI and DLP appliances, from analyzing the application layer data being sent and received. The PCAP files written to “/var/log/ReverseTlsProxy/” can be a valuable forensic asset when investigating an incident, but a real-time stream of the decrypted data is needed in order to swiftly detect and alert on potential security breaches and other incidents.

PolarProxy’s “--pcapoverip” option can be used to provide such a real-time stream of the decrypted data passing through the proxy. This data can easily be sent to a network interface using tcpreplay, as explained in our blog post “Sniffing Decrypted TLS Traffic with Security Onion”.

Security Considerations

The examples shown in this blog post all run PolarProxy with root privileges using sudo, which can be dangerous from a security perspective. PolarProxy is actually designed to be run without root privileges, but doing so prevents it from listening on a port below 1024. Luckily, this issue can easily be overcome with a simple port forwarding or redirect rule. The following iptables redirect rule can be used if PolarProxy is listening on TCP port 20443 and incoming HTTPS request are arriving to the eth0 interface of the proxy:

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -j REDIRECT --to 20443

PolarProxy does not support loading settings from a config file. The password for the PKCS12 certificate will therefore need to be supplied on the command line, which can make it visible from a process listing. If this is a concern for you, then please consider using “hidepid” to hide processes from other users. You can find instructions on how to use hidepid in hardening guides for Debian, Arch, SUSE and most other Linux flavors.

Posted by Erik Hjelmvik on Thursday, 12 March 2020 15:45:00 (UTC/GMT)

Tags: #PolarProxy #TLS #SSL #PCAP #decrypt #HTTPS #HTTP #HTTP/2 #http2 #IMAPS #decrypt

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RawCap Redux

RawCap A new version of RawCap has been released today. This portable little sniffer now supports writing PCAP data to stdout and named pipes as an alternative to saving the captured packets to disk. We have also changed the target .NET Framework version from 2.0 to 4.7.2, so that you can run RawCap on a modern Windows OS without having to install a legacy .NET Framework.

Here’s a summary of the improvements in the new RawCap version (0.2.0.0) compared to the old version (0.1.5.0):

  • Uses .NET 4.7.2 instead of 2.0
  • Support for writing to stdout
  • Support for writing to named pipes
  • Large (64 MB) ring buffer to prevent packet drops
  • Automatic firewall configuration

Out of the software we develop and maintain here at Netresec, NetworkMiner is the most popular one. But you’re probably not aware that RawCap is our second most popular tool in terms of downloads, with around 100 unique downloads every day. RawCap started out as just being a quick hack that we released for free to the community in 2011 without expecting it to gain much attention. However, it quickly gained popularity, maybe due to the fact that it’s just a tiny .exe file and that it doesn’t require any external libraries or DLL’s to sniff network traffic (other than the .NET Framework).

RawCap embraces the Unix philosophy to do only one thing, and do it well. Thanks to RawCap’s simplicity we have only needed to make a few minor updates of the tool since its first release 9 years ago. However, today we’re finally adding some new features that have been requested by users over the years. One such feature is that RawCap now automatically creates a Windows firewall rule when the tool is started. Before this feature was introduced users would have to run wf.msc (i.e. the "Windows Defender Firewall with Advanced Security") and manually create an inbound rule to allow RawCap.exe to receive incoming traffic. Without such a firewall rule RawCap would only be able to capture outgoing traffic.

RawCap can be started in two different modes. Either as an interactive console application, or as a “normal” command line utility. Run RawCap.exe without any arguments, or simply double click the RawCap.exe icon to use the interactive mode. You will then be asked which interface to capture packets from and what filename you’d like to save them to.

F:\Tools>RawCap.exe
Network interfaces:
0.     192.168.0.17    Local Area Connection
1.     192.168.0.47    Wireless Network Connection
2.     90.130.211.54   3G UMTS Internet
3.     192.168.111.1   VMware Network Adapter VMnet1
4.     192.168.222.1   VMware Network Adapter VMnet2
5.     127.0.0.1       Loopback Pseudo-Interface
Select network interface to sniff [default '0']: 1
Output path or filename [default 'dumpfile.pcap']:
Sniffing IP : 192.168.0.47
Output File : dumpfile.pcap
 --- Press [Ctrl]+C to stop ---
Packets     : 1337

The other alternative is to supply all the arguments to RawCap when it is started. Use “RawCap --help” to show which arguments you can use. You’ll need to use this mode if you want to write the captured traffic to standard output (stdout) or a named pipe, or if you want RawCap to automatically stop capturing after a certain time or packet count.

F:\Tools>RawCap.exe --help
NETRESEC RawCap version 0.2.0.0

Usage: RawCap.exe [OPTIONS] <interface> <pcap_target>
 <interface> can be an interface number or IP address
 <pcap_target> can be filename, stdout (-) or named pipe (starting with \\.\pipe\)

OPTIONS:
 -f          Flush data to file after each packet (no buffer)
 -c <count>  Stop sniffing after receiving <count> packets
 -s <sec>    Stop sniffing after <sec> seconds
 -m          Disable automatic creation of RawCap firewall entry
 -q          Quiet, don't print packet count to standard out

INTERFACES:
 0.     IP        : 169.254.63.243
        NIC Name  : Local Area Connection
        NIC Type  : Ethernet

 1.     IP        : 192.168.1.129
        NIC Name  : WiFi
        NIC Type  : Wireless80211

 2.     IP        : 127.0.0.1
        NIC Name  : Loopback Pseudo-Interface 1
        NIC Type  : Loopback

 3.     IP        : 10.165.240.132
        NIC Name  : Mobile 12
        NIC Type  : Wwanpp

Example 1: RawCap.exe 0 dumpfile.pcap
Example 2: RawCap.exe -s 60 127.0.0.1 localhost.pcap
Example 3: RawCap.exe 127.0.0.1 \\.\pipe\RawCap
Example 4: RawCap.exe -q 127.0.0.1 - | Wireshark.exe -i - -k

As you can see, running “RawCap.exe -s 60 127.0.0.1 localhost.pcap” will capture packets from localhost to a file called “localhost.pcap” for 60 seconds and then exit.

There are a couple of drawbacks with the new RawCap version though, it is a larger binary (48kB instead of 23kB) and it uses more CPU and RAM compared to the old version. We will therefore continue making the old RawCap version available to anyone who might need it.

Visit the RawCap product page to download this tool and learn more.

Posted by Erik Hjelmvik on Thursday, 30 January 2020 14:32:00 (UTC/GMT)

Tags: #Netresec #RawCap #sniffer #PCAP #named pipe #Wireshark #WiFi #loopback #127.0.0.1

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Sniffing Decrypted TLS Traffic with Security Onion

Wouldn't it be awesome to have a NIDS like Snort, Suricata or Zeek inspect HTTP requests leaving your network inside TLS encrypted HTTPS traffic? Yeah, we think so too! We have therefore created this guide on how to configure Security Onion to sniff decrypted TLS traffic with help of PolarProxy.

Network drawing with Clients, SecurityOnion and the Internet

PolarProxy is a forward TLS proxy that decrypts incoming TLS traffic from clients, re-encrypts it and forwards it to the server. One of the key features in PolarProxy is the ability to export the proxied traffic in decrypted form using the PCAP format (a.k.a. libpcap/tcpdump format). This makes it possible to read the decrypted traffic with external tools, without having to perform the decryption again. It also enables packet analysis using tools that don't have built-in TLS decryption support.

This guide outlines how to configure PolarProxy to intercept HTTPS traffic and send the decrypted HTTP traffic to an internal network interface, where it can be sniffed by an IDS.

STEP 1 ☆ Install Ubuntu

Download and install the latest SecurityOnion ISO image, but don't run the "Setup" just yet.

STEP 2 ☆ Add a Dummy Network Interface

Add a dummy network interface called "decrypted", to which decrypted packets will be sent.

ip link add decrypted type dummy
ip link set decrypted arp off up
Add the commands above to /etc/rc.local before "exit 0" to have the network interface automatically configured after reboots.

dummy interface in rc.local

STEP 3 ☆ Install Updates

Install updates in Security Onion by running "sudo soup".

STEP 4 ☆ Run the Security Onion Setup

Run the Security Onion setup utility by double-clicking the "Setup" desktop shortcut or executing "sudo sosetup" from a terminal. Follow the setup steps in the Production Deployment documentation and select "decrypted" as your sniffing interface.

Sniffing Interface Selection Window

Reboot and run Setup again to continue with the second phase of Security Onion's setup. Again, select "decrypted" as the interface to be monitored.

STEP 5 ☆ Install PolarProxy Service

Download and install PolarProxy:

sudo adduser --system --shell /bin/bash proxyuser
sudo mkdir /var/log/PolarProxy
sudo chown proxyuser:root /var/log/PolarProxy/
sudo chmod 0775 /var/log/PolarProxy/

sudo su - proxyuser
mkdir ~/PolarProxy
cd ~/PolarProxy/
curl https://www.netresec.com/?download=PolarProxy | tar -xzf -
exit

sudo cp /home/proxyuser/PolarProxy/PolarProxy.service /etc/systemd/system/PolarProxy.service

Edit /etc/systemd/system/PolarProxy.service and add "--pcapoverip 57012" at the end of the ExecStart command.

--pcapoverip 57012 in PolarProxy.service

Start the PolarProxy systemd service:

sudo systemctl enable PolarProxy.service
sudo systemctl start PolarProxy.service

STEP 6 ☆ Install Tcpreplay Service

The decrypted traffic can now be accessed via PolarProxy's PCAP-over-IP service on TCP 57012. We can leverage tcpreplay and netcat to replay these packets to our dummy network interface in order to have them picked up by Security Onion.

nc localhost 57012 | tcpreplay -i decrypted -t -
However, it's better to create a systemd service that does this automatically on bootup. We therefore create a file called /etc/systemd/system/tcpreplay.service with the following contents:
[Unit]
Description=Tcpreplay of decrypted traffic from PolarProxy
After=PolarProxy.service

[Service]
Type=simple
ExecStart=/bin/sh -c 'nc localhost 57012 | tcpreplay -i decrypted -t -'
Restart=on-failure
RestartSec=3

[Install]
WantedBy=multi-user.target

Start the tcpreplay systemd service:

sudo systemctl enable tcpreplay.service
sudo systemctl start tcpreplay.service

STEP 7 ☆ Add firewall rules

Security Onion only accepts incoming connections on TCP 22 by default, we also need to allow connections to TCP port 10443 (proxy port), and 10080 (root CA certificate download web server). Add allow rules for these services to the Security Onion machine's firewall:

sudo ufw allow in 10443/tcp
sudo ufw allow in 10080/tcp

Verify that the proxy is working by running this curl command on a PC connected to the same network as the Security Onion machine:

curl --insecure --connect-to www.netresec.com:443:[SecurityOnionIP]:10443 https://www.netresec.com/
Note: You can even perform this test from a Win10 PC, since curl is included with Windows 10 version 1803 and later.

Add the following lines at the top of /etc/ufw/before.rules (before the *filter section) to redirect incoming packets on TCP 443 to PolarProxy on port 10443.

*nat
:PREROUTING ACCEPT [0:0]
-A PREROUTING -i enp0s3 -p tcp --dport 443 -j REDIRECT --to 10443
COMMIT

Note: Replace "enp0s3" with the Security Onion interface to which clients will connect.

After saving before.rules, reload ufw to activate the port redirection:

sudo ufw reload

Verify that you can reach the proxy on TCP 443 with this command:

curl --insecure --resolve www.netresec.com:443:[SecurityOnionIP] https://www.netresec.com/

STEP 8 ☆ Redirect HTTPS traffic to PolarProxy

It's now time to configure a client to run its HTTPS traffic through PolarProxy. Download and install the PolarProxy X.509 root CA certificate from PolarProxy's web service on TCP port 10080:

http://[SecurityOnionIP]:10080/polarproxy.cer

Install the certificate in the operating system and browser, as instructed in the PolarProxy documentation.

You also need to forward packets from the client machine to the Security Onion machine running PolarProxy. This can be done either by configuring a local NAT rule on each monitored client (STEP 8.a) or by configuring the default gateway's firewall to forward HTTPS traffic from all clients to the proxy (STEP 8.b).

STEP 8.a ☆ Local NAT

Use this firewall rule on a Linux client to configure it to forward outgoing HTTPS traffic to the Security Onion machine:

sudo iptables -t nat -A OUTPUT -p tcp --dport 443 -j DNAT --to [SecurityOnionIP]

STEP 8.b ☆ Global NAT Network drawing Firewall, PolarProxy, Clients

If the client isn't running Linux, or if you wanna forward HTTPS traffic from a whole network to the proxy, then apply the following iptables rules to the firewall in front of the client network. See "Routing Option #2" in the PolarProxy documentation for more details.

  1. Add a forward rule on the gateway to allow forwarding traffic to our PolarProxy server:
    sudo iptables -A FORWARD -i eth1 -d [SecurityOnionIP] -p tcp --dport 10443 -m state --state NEW -j ACCEPT
  2. Add a DNAT rule to forward 443 traffic to PolarProxy on port 10443:
    sudo iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 443 -j DNAT --to [SecurityOnionIP]:10443
  3. If the reverse traffic from PolarProxy to the client doesn't pass the firewall (i.e. they are on the same LAN), then we must add this hide-nat rule to fool PolarProxy that we are coming from the firewall:
    sudo iptables -t nat -A POSTROUTING -o eth1 -d [SecurityOnionIP] -p tcp --dport 10443 -j MASQUERADE
For other network configurations, please see the various routing setups in the PolarProxy documentation.

STEP 9 ☆ Inspect traffic in SecurityOnion

Wait for the Elastic stack to initialize, so that the intercepted network traffic becomes available through the Kibana GUI. You can check the status of the elastic initialization with "sudo so-elastic-status".

You should now be able to inspect decrypted traffic in Security Onion using Kibana, Squert, Sguil etc., just as if it was unencrypted HTTP.

Bro HTTP traffic in Kibana Image: Kibana showing HTTP traffic info from decrypted HTTPS sessions

MIME types in Kibana Image: MIME types in Kibana

NIDS alerts in Kibana Image: NIDS alerts from payload in decrypted traffic shown in Kibana

Snort alerts in Squert Image: Snort alerts from decrypted traffic shown in Squert

Security Considerations and Hardening

Security Onion nodes are normally configured to only allow access by SOC/CERT/CSIRT analysts, but the setup described in this blog post requires that "normal" users on the client network can access the PolarProxy service running on the Security Onion node. We therefore recommend installing PolarProxy on a dedicated Security Onion Forward Node, which is configured to only monitor traffic from the proxy.

We also recommend segmenting the client network from the analyst network, for example by using separate network interfaces on the Security Onion machine or putting it in a DMZ. Only the PolarProxy service (TCP 10080 and 10443) should be accessable from the client network.

PolarProxy could be used to pivot from the client network into the analyst network or to access the Apache webserver running on the Security Onion node. For example, the following curl command can be used to access the local Apache server running on the Security Onion machine via PolarProxy:

curl --insecure --connect-to localhost:443:[SecurityOnionIP]:10443 https://localhost/
We therefore recommend adding firewall rules that prevent PolarProxy from accessing the analyst network as well as the local Apache server.

Hardening Steps:

  • Configure the Security Onion node as a Forward Node
  • Segment client network from analyst network
  • Add firewall rules to prevent PolarProxy from accessing services on the local machine and analyst network

For additional info on hardening, please see the recommendations provided by Wes Lambert on the Security-Onion mailing list.

Posted by Erik Hjelmvik on Monday, 20 January 2020 09:40:00 (UTC/GMT)

Tags: #SecurityOnion #Security Onion #PCAP #Bro #PolarProxy #Snort #Suricata #TLS #SSL #HTTPS #tcpreplay #PCAP-over-IP #IDS #NIDS #netcat #curl

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Sharing a PCAP with Decrypted HTTPS

Modern malware and botnet C2 protocols use TLS encryption in order to blend in with "normal" web traffic, sometimes even using legitimate services like Twitter or Instagram.

I did a live demo at the CS3Sthlm conference last year, titled "TLS Interception and Decryption", where I showed how TLS interception can be used to decrypt and analyze malicious HTTPS network traffic. During the demo I used DNS-over-HTTPS (DoH) and posted messages to Pastebin and Twitter, pretending to be a malware or malicious actor. The HTTPS network traffic was decrypted and analyzed live as part of my demo. The CS3Sthlm organizers have posted a video recording of the live demo on YouTube.

Erik presenting PolarProxy at CS3Sthlm, photo credit: CS3Sthlm

Image: Erik demoing TLS Interception and Decryption at CS3Sthlm 2019

We are now releasing a PCAP file with the decrypted network traffic captured during this live demo here:

» https://www.netresec.com/files/proxy-191023-091924.pcap «

This blog post provides a step-by-step walk-through of the decrypted HTTPS traffic in the released capture file.

The TLS decryption was performed by connecting a laptop to a custom WiFi access point, which was a Raspberry Pi configured as in our "Raspberry Pi WiFi Access Point with TLS Inspection" blog post. I additionally enabled the PCAP-over-IP feature in PolarProxy by starting it with the "--pcapoverip 57012" option. This allowed me to connect with Wireshark and NetworkMiner to TCP port 57012 on the TLS proxy and stream the decrypted traffic in order to perform live network traffic analysis.

Laptop, Raspberry Pi, PolarProxy, Internet ASCII

Image: Live demo network with Laptop (Browser, NetworkMiner, Wireshark), Raspberry Pi (PolarProxy) and the Internet.

Below follows a breakdown of various significant events of my demo and where you can find these events in the released capture file.

DNS lookup of "www.google.com" using DoH

  • Frame: 833
  • Protocol: DoH using HTTP/2 POST
  • Five tuple: 192.168.4.20:52694 104.16.248.249:80 TCP
DoH lookup of www.google.com shown in NetworkMiner DoH lookup of www.google.com shown in Wireshark

Google search for "tibetan fox psbattle"

  • Frame: 2292
  • Protocol: HTTP/2
  • Five tuple: 192.168.4.20:52716 216.58.211.4:80 TCP
Google search for 'tibetan fox psbattle' in Wireshark Google search for 'tibetan fox psbattle' in NetworkMiner

Tibetan Fox image downloaded from reddit

  • Frame: 3457
  • Protocol: HTTP/2
  • Five tuple: 192.168.4.20:52728 151.101.85.140:80 TCP
Image download from reddit shown in NetworkMiner

Orginal "tibetan fox" image downloaded from this reddit thread.

Tibetan Fox Remix Image HTTP/2 Download

  • Frame: 5805
  • Protocol: HTTP/2
  • Five tuple: 192.168.4.20:52769 151.101.84.193:80 TCP
Images downloaded via HTTP/2

DNS Lookup of "cs3sthlm.se"

  • Frame: 13494
  • Protocol: DoH using HTTP/2 POST
  • Five tuple: 192.168.4.20:52699 104.16.249.249:80 TCP

Images downloaded from CS3Sthlm's website

  • Frame: 14134
  • Protocol: HTTP/1.1
  • Five tuple: 192.168.4.20:52896 192.195.142.160:80 TCP
Images downloaded from CS3Sthlm's website

Data sent in HTTP/2 POST to Pastebin

  • Frame: 18572
  • Protocol: HTTP/2 POST
  • Five tuple: 192.168.4.20:52904 104.22.2.84:80 TCP
Data sent to Pastebin in HTTP/2 POST

The file "post.php.form-data" contains the data sent to Pastebin in the HTTP/2 POST request. Here are the reassembled contents of that file, including the "hello cs3 I am a malware" message:

-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="csrf_token_post"

MTU3MTgyMjg5OTFwcjBzODJaQ0NuUk9PT1B3ZTl0b20zdFg3ZkhXQ1R4
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="submit_hidden"

submit_hidden
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="paste_code"

hello cs3 I am a malware
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="paste_format"

1
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="paste_expire_date"

1H
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="paste_private"

0
-----------------------------54168074520069581482009826076
Content-Disposition: form-data; name="paste_name"

malware traffic
-----------------------------54168074520069581482009826076--

Mallory80756920 logs in to Twitter

  • Frame: 24881
  • Protocol: HTTP/2 POST
  • Five tuple: 192.168.4.20:53210 104.244.42.65:80 TCP
Twitter credentials for Mallory80756920

Mallory80756920 posts a Tweet

  • Frame: 26993
  • Protocol: HTTP/2 POST
  • Five tuple: 192.168.4.20:53251 104.244.42.66:80 TCP

Mallory80756920 tweeted "Hello CS3! I'm in you!". The data was sent to twitter using an HTTP/2 POST request.

Twitter post in Wireshark Twitter post in NetworkMiner

Conclusions

A great deal of the interesting TLS traffic in the analyzed capture file is using the HTTP/2 protocol. This doesn't come as a surprise since more than half of all HTTPS traffic is using HTTP/2 nowadays (sources: server protocol statistics, client protocol statistics). It is therefore essential to be able to analyze HTTP/2 traffic if you have a TLS inspection (TLSI) solution in place. Unfortunately many TLSI products don't yet support the HTTP/2 protocol.

Wireshark was one of the first network traffic analysis tools to implement HTTP/2 support, much thanks to Alexis La Goutte. However, Wireshark's excellent "File > Export Objects" doesn't yet support extraction of files from HTTP/2 traffic. There are other ways to extract HTTP/2 file transfers with Wireshark, but they require a few additional steps in order to carve out the file to disk.

Luckily NetworkMiner extracts files from HTTP/2 as of version 2.5. In fact, we believe NetworkMiner is the first open source tool to support automatic HTTP/2 file extraction from PCAP.

Finally, I'd like to stress the point that modern malware use HTTPS, so you need to have a TLSI solution in place to analyze the malicious traffic. As the majority of all HTTPS traffic is using HTTP/2 you also need to ensure that you're able to analyze HTTP/2 traffic passing through your TLSI solution.

Posted by Erik Hjelmvik on Monday, 13 January 2020 12:45:00 (UTC/GMT)

Tags: #HTTP/2 #http2 #DoH #TLS #Google #decrypt #HTTPS #TLSI #TLS Inspection #TLS Interception #PolarProxy #NetworkMiner #Wireshark #CS3Sthlm #CS3 #Forensics #PCAP #Video

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Installing a Fake Internet with INetSim and PolarProxy

INetSim + PolarProxy

This is a tutorial on how to set up an environment for dynamic malware analysis, which can be used to analyze otherwise encrypted HTTPS and SMTPS traffic without allowing the malware to connect to the Internet. Dynamic malware analysis (or behavioral analysis) is performed by observing the behavior of a malware while it is running. The victim machine, which executes the malware, is usually a virtual machine that can be rolled back to a clean state when the analysis is complete. The safest way to prevent the malware from infecting other machines, or doing other bad things like sending SPAM or taking part in DDoS attacks, is to run the victim machine in an offline environment. However, network traffic analysis of malware is a central part of dynamic malware analysis, which is is why a “fake Internet” is needed in most malware labs.

INetSim and PolarProxy

INetSim is a software suite that simulates common internet services like HTTP, DNS and SMTP, which useful when analyzing the network behavior of malware samples without connecting them to the Internet. INetSim also has basic support for TLS encrypted protocols, like HTTPS, SMTPS, POP3S and FTPS, but requires a pre-defined X.509-certificate to be loaded at startup. This can cause malware to terminate because the Common Names (CN) in the presented certificates don’t match the requested server names. The victim machine will actually get the exact same certificate regardless of which web site it visits. INetSim’s TLS encryption also inhibits analysis of the network traffic captured in the malware lab, such as C2 traffic or SPAM runs, because the application layer traffic is encrypted. PolarProxy can solve both these issues because it generates certificates on the fly, where the CN value is dynamically set to the requested host name, and saves the network traffic in decrypted form to PCAP files. It is therefore a good idea to replace the TLS services in INetSim with PolarProxy, which will be used as a TLS termination proxy that forwards the decrypted traffic to INetSim’s cleartext services.

Malware Lab Setup

Install Linux

The first step is to install a Linux VM, which will act as a fake Internet to the victim machine(s). I'm using Ubuntu Server 18.04.3 LTS in this tutorial, but you can use any 64-bit linux distro. I'm adding two network interfaces to the Linux VM, one interface with Internet access and one that connects to an isolated offline network to which the victim VM's will be connected. The offline interface is configured to use the static IP 192.168.53.19.

Important: Do not bridge, bond or enable IP forwarding between the two interfaces!

Network connection config Ubuntu Server 18.04

Install INetSim

INetSim is available in Ubuntu's repo, so it is possible to install it with "apt install inetsim". However, I recommend installing INetSim as described in the official documentation to get the latest packaged version of INetSim.

sudo -s

echo "deb http://www.inetsim.org/debian/ binary/" > /etc/apt/sources.list.d/inetsim.list

curl https://www.inetsim.org/inetsim-archive-signing-key.asc | apt-key add -

apt update

apt install inetsim

exit

INetSim listens on 127.0.0.1 by default, change this to INetSim's offline IP address by un-commenting and editing the service_bind_address variable in /etc/inetsim/inetsim.conf.

service_bind_address    192.168.53.19

Also configure INetSim's fake DNS server to resolve all domain names to the IP of INetSim with the dns_default_ip setting:

dns_default_ip    192.168.53.19

Finally, disable the "start_service https" and "start_service smtps" lines, because these services will be replaced with PolarProxy:

start_service dns
start_service http
#start_service https
start_service smtp
#start_service smtps

Restart the INetSim service after changing the config.

sudo systemctl restart inetsim.service

Verify that you can access INetSim's HTTP server with curl:

curl http://192.168.53.19

<html>
  <head>
    <title>INetSim default HTML page</title>
  </head>
  <body>
    <p></p>
    <p align="center">This is the default HTML page for INetSim HTTP server fake mode.</p>
    <p align="center">This file is an HTML document.</p>
  </body>
</html>

It looks like INetSim's web server can be accessed alright.

Install PolarProxy

Next step is to install PolarProxy as a systemd service (as instructed here):

sudo adduser --system --shell /bin/bash proxyuser

sudo mkdir /var/log/PolarProxy

sudo chown proxyuser:root /var/log/PolarProxy/

sudo chmod 0775 /var/log/PolarProxy/

sudo su - proxyuser

mkdir ~/PolarProxy

cd ~/PolarProxy/

curl https://www.netresec.com/?download=PolarProxy | tar -xzvf -

exit

sudo cp /home/proxyuser/PolarProxy/PolarProxy.service /etc/systemd/system/PolarProxy.service

We will need to modify the PolarProxy service config file a bit before we start it. Edit the ExecStart setting in /etc/systemd/system/PolarProxy.service to configure PolarProxy to terminate the TLS encryption for HTTPS and SMTPS (implicitly encrypted email submission). The HTTPS traffic should be redirected to INetSim's web server on tcp/80 and the SMTPS to tcp/25.

ExecStart=/home/proxyuser/PolarProxy/PolarProxy -v -p 10443,80,80 -p 10465,25,25 -x /var/log/PolarProxy/polarproxy.cer -f /var/log/PolarProxy/proxyflows.log -o /var/log/PolarProxy/ --certhttp 10080 --terminate --connect 192.168.53.19 --nosni nosni.inetsim.org

Here's a break-down of the arguments sent to PolarProxy through the ExecStart setting above:

  • -v : verbose output in syslog (not required)
  • -p 10443,80,80 : listen for TLS connections on tcp/10443, save decrypted traffic in PCAP as tcp/80, forward traffic to tcp/80
  • -p 10465,25,25 : listen for TLS connections on tcp/10465, save decrypted traffic in PCAP as tcp/25, forward traffic to tcp/25
  • -x /var/log/PolarProxy/polarproxy.cer : Save certificate to be imported to clients in /var/log/PolarProxy/polarproxy.cer (not required)
  • -f /var/log/PolarProxy/proxyflows.log : Log flow meta data in /var/log/PolarProxy/proxyflows.log (not required)
  • -o /var/log/PolarProxy/ : Save PCAP files with decrypted traffic in /var/log/PolarProxy/
  • --certhttp 10080 : Make the X.509 certificate available to clients over http on tcp/10080
  • --terminate : Run PolarProxy as a TLS termination proxy, i.e. data forwarded from the proxy is decrypted
  • --connect 192.168.53.19 : forward all connections to the IP of INetSim
  • --nosni nosni.inetsim.org : Accept incoming TLS connections without SNI, behave as if server name was "nosni.inetsim.org".

Finally, start the PolarProxy systemd service:

sudo systemctl enable PolarProxy.service

sudo systemctl start PolarProxy.service

Verify that you can reach INetSim through PolarProxy's TLS termination proxy using curl:

curl --insecure --connect-to example.com:443:192.168.53.19:10443 https://example.com

<html>
  <head>
    <title>INetSim default HTML page</title>
  </head>
  <body>
    <p></p>
    <p align="center">This is the default HTML page for INetSim HTTP server fake mode.</p>
    <p align="center">This file is an HTML document.</p>
  </body>
</html>

Yay, it is working! Do the same thing again, but also verify the certificate against PolarProxy's root CA this time. The root certificate is downloaded from PolarProxy via the HTTP service running on tcp/10080 and then converted from DER to PEM format using openssl, so that it can be used with curl's "--cacert" option.

curl http://192.168.53.19:10080/polarproxy.cer > polarproxy.cer

openssl x509 -inform DER -in polarproxy.cer -out polarproxy-pem.crt

curl --cacert polarproxy-pem.crt --connect-to example.com:443:192.168.53.19:10443 https://example.com

<html>
  <head>
    <title>INetSim default HTML page</title>
  </head>
  <body>
    <p></p>
    <p align="center">This is the default HTML page for INetSim HTTP server fake mode.</p>
    <p align="center">This file is an HTML document.</p>
  </body>
</html>

Yay #2!

Now let's set up routing to forward all HTTPS traffic to PolarProxy's service on tcp/10443 and SMTPS traffic to tcp/10465. I'm also adding a firewall rule to redirect ALL other incoming traffic to INetSim, regardless of which IP it is destined to, with the final REDIRECT rule. Make sure to replace "enp0s8" with the name of your interface.

sudo iptables -t nat -A PREROUTING -i enp0s8 -p tcp --dport 443 -j REDIRECT --to 10443

sudo iptables -t nat -A PREROUTING -i enp0s8 -p tcp --dport 465 -j REDIRECT --to 10465

sudo iptables -t nat -A PREROUTING -i enp0s8 -j REDIRECT

Verify that the iptables port redirection rule is working from another machine connected to the offline 192.168.53.0/24 network:

curl --insecure --resolve example.com:443:192.168.53.19 https://example.com

<html>
  <head>
    <title>INetSim default HTML page</title>
  </head>
  <body>
    <p></p>
    <p align="center">This is the default HTML page for INetSim HTTP server fake mode.</p>
    <p align="center">This file is an HTML document.</p>
  </body>
</html>

Yay #3!

curl --insecure --resolve example.com:465:192.168.53.19 smtps://example.com

214-Commands supported:
214- HELO MAIL RCPT DATA
214- RSET NOOP QUIT EXPN
214- HELP VRFY EHLO AUTH
214- ETRN STARTTLS
214 For more info use "HELP <topic>".

Yay #4!

It is now time to save the firewall rules, so that they will survive reboots.

sudo apt-get install iptables-persistent

Install the Victim Windows PC

Configure a static IP address on the victim Windows host by manually setting the IP address. Set the INetSim machine (192.168.53.19) as the default gateway and DNS server.

Windows IPv4 Properties

Download the X.509 root CA certificate from your PolarProxy installation here: http://192.168.53.19:10080/polarproxy.cer

  1. Double-click on "polarproxy.cer"
  2. Click [Install Certificate...]
  3. Select 🔘 Local Machine and press [Next]
  4. Select 🔘 Place all certificates in the following store and press [Browse...]
  5. Choose "Trusted Root Certification Authorities" and press [OK], then [Next]
  6. Press [Finish]

You might also want to install the PolarProxy certificate in your browser. This is how you install it to Firefox:

  1. Options / Preferences
  2. Press [Privacy & Security]
  3. Scroll down to "Certificates" and press [View Certificates...]
  4. In the "Authorities" tab, press [Import...]
  5. Open "polarproxy.cer"
  6. ☑ Trust this CA to identify websites. (check the box)
  7. Press [OK]

Now, open a browser and try visiting some websites over HTTP or HTTPS. If you get the following message regardless of what domain you try to visit, then you've managed to set everything up correctly:

This is the default HTML page for INetSim HTTP server fake mode.

This file is an HTML document.

Accessing the Decrypted Traffic

PCAP files with decrypted HTTPS and SMTPS traffic are now available in /var/log/PolarProxy/

PolarProxy will start writing to a new capture file every 60 minutes. However, the captured packets are not written to disk instantly because PolarProxy uses buffered file writing in order to improve performance. You can restart the proxy service if you wish to flush the buffered packets to disk and have PolarProxy rotate to a new capture file.

sudo systemctl restart PolarProxy

I also recommend capturing all network traffic sent to INetSim with a sniffer like netsniff-ng. This way you’ll get PCAP files with traffic from INetSim’s cleartext services (like DNS and HTTP) as well.

PCAP or it didn’t happen!

Credits

I'd like to thank Thomas Hungenberg and Patrick Desnoyers for providing valuable feedback for this blog post!

Posted by Erik Hjelmvik on Monday, 09 December 2019 08:40:00 (UTC/GMT)

Tags: #PolarProxy #HTTPS #SMTPS #HTTP #SMTP #DNS #Malware #TLS #PCAP #tutorial

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The NSA HSTS Security Feature Mystery

NSA TLSI advisory header

I recently stumbled across an NSA Cyber Advisory titled Managing Risk from Transport Layer Security Inspection (U/OO/212028-19) after first learning about it through Jonas Lejon’s blog post NSA varnar för TLS-inspektion (Swedish). I read the NSA report with great interest since I wanted to see how our own TLS interception tool PolarProxy stands up to the risks identified in the advisory.

I highly respect the NSA’s knowledge in the fields of cryptography and security, which is why I read the advisory as if it was the definite guide on how to perform TLS inspection in a secure manner. However, towards the end of the advisory I got stuck on this paragraph, which I was unable to understand:

HTTP Strict Transport Security (HSTS) includes a security feature that binds the HTTP session to the specific TLS session used. TLSI systems that ignore the underlying HTTP headers will cause HSTS sessions to be rejected by the client application, the server, or both.

WUT?!?! HSTS (RFC 6797) is designed to protect against attacks like Moxie Marlinspike’s 10 year old sslstrip, which fools the client into using unencrypted HTTP instead of HTTPS. As far as I know, HSTS does not support binding an HTTP session to a specific TLS session.

What is HSTS?

HSTS is a simple HTTP header sent by the web server to inform the browser that it should only load the site using HTTPS. The header can look like this:

strict-transport-security: max-age=47111337; includeSubDomains; preload

NetworkMiner 2.5 showing HSTS headers from HTTP/1.1 and HTTP/2 traffic

Image: NetworkMiner 2.5 showing HSTS headers from HTTP/1.1 and HTTP/2 traffic

The PCAP file loaded into NetworkMiner in screenshot above contains HTTPS traffic that has been decrypted by PolarProxy. You can also use Wireshark or tshark to find HSTS headers by using the following display filter:

http.response.line matches "Strict-Transport-Security" or http2.header.name matches "Strict-Transport-Security"

Notice the use of “matches” to get case insensitive matching of “Strict-Transport-Security” and the duplicated statements required to get the filter to match headers in both HTTP/1.1 and HTTP/2.

Back to the NSA Advisory

I simply couldn’t understand NSA’s statement about the HSTS “security feature” that binds the HTTP session to the specific TLS session used, because I’m not aware of any such feature in HSTS and my google-fu was to weak to find any such feature. I therefore resorted to asking folks on Twitter if they knew about this feature.

Nick Sullivan (Head of Research and Cryptography at Cloudflare) kindly replied on twitter that they probably mean “Token Binding” (RFC 8471). Peter Wu (Wireshark core developer and TLS expert) additionally replied that the NSA perhaps were referring to the Sec-Token-Binding header name in RFC 8473 (which has nothing to do with HSTS).

Backed by these two experts in TLS and HTTPS I can confidently conclude that the authors of the NSA’s Transport Layer Security Inspection (TLSI) advisory have either misunderstood what HSTS is or made some form of typo. I have reported this error to the NSA, but have not yet received any response.

Other Issues in NSA’s TLSI Advisory

This experience dented my faith in the TLS expertise of the NSA in general and in particular the authors of this advisory. I therefore decided to re-read the TLSI advisory, but this time without the “NSA knows this stuff” glasses I had on before. This time I found several additional claims and statements, which I didn’t agree with, in the four page advisory.

To start with, the first figure in the document depicts two setups where one is allowing end-to-end encryption between the client and server, while the other is using TLS inspection.

Encrypted Traffic (top) and TLS Inspection (bottom) as shown in NSA’s TLSI advisory

Image: Encrypted Traffic (top) and TLS Inspection (bottom) as shown in NSA’s TLSI advisory

In the end-to-end setup we see the malicious traffic passing straight to the client, while in the second setup the malicious traffic is blocked by the TLSI device. This image is accompanied by the following text:

A TLSI capability implemented within a forward proxy between the edge of the enterprise network and an external network such as the Internet protects enterprise clients from the high risk environment outside the forward proxy.

My experience is that blocking traffic in this way is more likely to provide a false sense of security than improved protection against malware. It is better to use TLSI to detect intrusions than to try to block them.

This probably sounds counter-intuitive, as you might reason that “if you can detect it, why can't you prevent it?”. I’m not going to go into a lengthy explanation of the “Prevention Eventually Fails” paradigm here, instead I’d recommend reading Richard Bejtlichs book “The Tao of Network Security Monitoring” or his more recent book “The Practice of Network Security Monitoring”. You can also read Richards blog post about ”The Problem with Automated Defenses” or Phil Hagen’s “What to Do When Threat Prevention Fails”.

TLSI products should primarily be used to provide visibility in order to detect and respond to malware and intrusions. Many TLSI products can block some attacks, but they don’t really provide perimeter security. Unfortunately the NSA advisory might further strengthen this false sense of security with the mentioned image and accompanying text.

DO IT WELL, DO IT ONCE

The NSA advisory states:

To minimize the risks described above, breaking and inspecting TLS traffic should only be conducted once within the enterprise network. Redundant TLSI, wherein a client-server traffic flow is decrypted, inspected, and re-encrypted by one forward proxy and is then forwarded to a second forward proxy for more of the same, should not be performed.

In general, I agree with this statement. Unfortunately many TLSI products do not “do it well”, which is why “do it once” is not always enough. One such situation is when a PC is believed to be infected with malware, but further investigation is required to know for sure. Many TLSI products apply lock-in techniques that prevent incident responders from analyzing the decrypted traffic with external tools. This forces IR teams to add an extra TLS proxy when their enterprise TLSI product does not provide sufficient visibility. PolarProxy is, in fact, designed to support that type of agile TLSI deployment, in order to enable decryption and inspection of TLS traffic from a particular machine during an incident.

Final Words about the Advisory and TLS Inspection

Even through this blog post criticizes parts of the NSA TLSI advisory, I’d still like to end with saying that it also brings a lot of good stuff to the table. The issues mentioned in this blog post are actually just minor ones, which hopefully won’t have any negative impact on future TLSI deployments. In fact, the positive aspects of the advisory by far outweighs the negative ones. I also hope this blog post can help get more discussions going about TLS inspection, such as if we need it, what problems it can solve and what risks we take by deploying it.

UPDATE, 16 December 2019

The NSA released an updated version of the advisory today (1U/OO/212028-19). The advisory now says:

  • TLS Token Binding binds security tokens to the specific TLS session used. TLSI systems can cause the sessions or tokens to be rejected by the client application, the server, or both.
  • Hypertext Transfer Protocol Strict Transport Security (HSTS) requires that Hypertext Transfer Protocol over TLS (HTTPS) is used in the future with trusted certificates and that all content is received via HTTPS as well. If a TLS client application attempts to follow the HSTS requirements but does not trust the separate TLSI CA, the client will reject the TLSI sessions and prevent users from clicking-through browser warnings.

Thanks for updating!

Posted by Erik Hjelmvik on Tuesday, 26 November 2019 19:18:00 (UTC/GMT)

Tags: #TLSI #TLS Inspection #TLS Interception #PolarProxy #TLS #NetworkMiner #Wireshark

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Extracting Kerberos Credentials from PCAP

NetworkMiner + Cerberos

NetworkMiner is one of the best tools around for extracting credentials, such as usernames and passwords, from PCAP files. The credential extraction feature is primarily designed for defenders, in order to analyze credential theft and lateral movement by adversaries inside your networks. But the credential extraction feature is also popular among penetration testers. In this blog post I will demo how Kerberos hashes can be extracted from captured network traffic with NetworkMiner, and how these hashes can be cracked in order to retrieve the clear text passwords.

Installing NetworkMiner in Kali Linux

I’m using a clean install of Kali Linux 2019.3, on which I have installed NetworkMiner by following the step-by-step instructions in our guide for installing NetworkMiner in Ubuntu, Fedora and Arch Linux.

NetworkMiner 2.5 in Kali Linux

Extracting Kerberos Hashes from PCAP

There is a capture file in Wireshark’s sample captures called krb-816.cap. This capture file contains Kerberos traffic from a Windows XP machine, as two user accounts perform a domain logon. Let’s download that PCAP file and open it in NetworkMiner.

wget 'https://wiki.wireshark.org/SampleCaptures?action=AttachFile&do=get&target=krb-816.zip' -O krb-816.zip
unzip krb-816.zip
/opt/NetworkMiner_2-5/NetworkMiner.exe krb-816.cap

The “Credentials” tab contains the extracted Kerberos hashes. Right-click on the first $krb5pa$23$ hash and select “Copy Password” to put the password into the system clipboard.

Copy Kerberos hash to system clipboard in Linux

Paste the password to a text file, either using a text editor or directly from a shell.

Note: You'll need to do press Ctrl+Shift+Insert in GNOME Terminal to paste from the system clipboard, which is where NetworkMiner has put the password.

echo '$krb5pa$23$des$DENYDC$$32d396a914a4d0a78e979ba75d4ff53c1db7294141760fee05e434c12ecf8d5b9aa5839e09a2244893aff5f384f79c37883f154a' > krb5pa.hash

You can now try to crack the hash, for example by running John the Ripper (JtR) or hashcat.

john krb5pa.hash
Using default input encoding: UTF-8
Loaded 1 password hash (krb5pa-md5, Kerberos 5 AS-REQ Pre-Auth etype 23 [32/64])
[...]
Use the "--show" option to display all of the cracked passwords reliably
Session completed
john krb5pa.hash --show
?:123

1 password hash cracked, 0 left

Yay! We now know that the password of user “des” was “123”. Let’s try to recover the password of the user “u5” as well, but this time we’ll use the $krb5asrep$23$ hash.

Copying the krb5asrep hash from NetworkMiner
john krb5asrep.hash
[...]
john krb5asrep.hash --show
?:123

1 password hash cracked, 0 left

Apparently the password for user u5 was “123” as well.

If you wanna replace JtR with hashcat, then make sure to use the following hash modes:

  • $krb5pa$23$: hashcat -m 7500
  • $krb5tgs$23$: hashcat -m 13100
  • $krb5asrep$23$: hashcat -m 18200
For other hash types, please see the hashcat example hashes.

Running the Command Line version of NetworkMiner

The commercial version of NetworkMiner comes with a command line tool called NetworkMinerCLI. You can extract the Kerberos hashes from a PCAP file and save them to a CSV file using NetworkMinerCLI like this:

/opt/NetworkMinerProfessional_2-5/NetworkMinerCLI.exe -r krb-816.cap -f CSV_NoNewlines
Closing file handles...
32 frames parsed in 0.1337 seconds.

NetworkMinerCLI has now created a set of CSV files, one for each type/class of information found in the capture file. In this case we want the krb-816.cap.Credentials.csv file, in which the hashes and passwords are in column 5:

cut -d, -f5 krb-816.cap.Credentials.csv
"Password"
"$krb5pa$23$des$DENYDC$$32d396a914a4d0a78e979ba75d4ff53c1db7294141760fee05e434c12ecf8d5b9aa5839e09a2244893aff5f384f79c37883f154a"
"$krb5pa$3$des$DENYDC$DENYDC.COMdes$233b4272aa93727221facfdbdcc9d1d9a0c43a2798c810600310c0daf48fb969c26cb47d69f575a65e00163845f68811f9c5266271cc0f91"
"$krb5asrep$3$DENYDC.COMdes$edbcc0d67f3a645254f086e6$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"
[...]

Posted by Erik Hjelmvik on Thursday, 14 November 2019 12:25:00 (UTC/GMT)

Tags: #PCAP #Kerberos #Linux #hashcat #John #NetworkMinerCLI

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NetworkMiner 2.5 Released

NetworkMiner 2.5

I am happy to announce the release of NetworkMiner 2.5 today! This new version includes new features like JA3 and parsers for the HTTP/2 and DoH protocols. We have also added support for a few older protocols that are still widely used, such as Kerberos and the CIFS browser protocol. Additionally, NetworkMiner can now parse PCAP files up to twice as fast as before!

Improving Passive TLS Analysis with JA3

Almost all web traffic is TLS encrypted nowadays, which prevents incident responders, analysts and investigators from inspecting otherwise unencrypted HTTP traffic for clues about malicious behavior or criminal intent. This requires analysts to use alternative approaches, such as looking at hostnames and X.509 certificates. This type of analysis is supported by NetworkMiner, since it parses Server Name Indication fields in client TLS handshakes and extracts X.509 certificates automatically when PCAP files are loaded.

In this release we’ve also added support for another passive TLS analysis technique called JA3, which is a method for fingerprinting TLS client implementations.

NetworkMiner leverages the JA3 fingerprint database from Trisul Network Analytics in order to match observed JA3 hashes to hashes of known malware and “normal” applications. This is what it looks like when the capture file “snort.log.1428364808”, from the FIRST 2015 “Hands-on Network Forensics” training (available here), has been loaded into NetworkMiner 2.5:

JA3 fingerprint of a Skype client

Image: JA3 fingerprint of a Skype client in NetworkMiner 2.5

The JA3 hash is also available in the “Parameters” tab, which is useful in order to find out what hosts that particular TLS implementation was reaching out to.

Filtering on JA3 hash 06207a1730b5deeb207b0556e102ded2 in NetworkMiner 2.5

Image: Filtering on JA3 hash 06207a1730b5deeb207b0556e102ded2

HTTP/2 and DoH Support

Passive analysis of TLS traffic, such as HTTPS, often doesn’t give sufficient visibility. Many organizations therefore use TLS proxies in order to decrypt the traffic going in and out from their networks. However, more than half of all HTTPS traffic is actually http2 (RFC 7540) nowadays. This has previously been an issue for users who wanted to analyze decrypted http2 traffic from their TLS intercepting proxies with NetworkMiner. We’re happy to announce that NetworkMiner now can parse http2 traffic, that has been decrypted by a TLS proxy, and extract files from the http2 transfers.

NetworkMiner 2.5 also supports the DNS over HTTPS (DoH) protocol (RFC 8484), which is a technique for sending DNS queries as http2 POST requests and parsing the returned data as DNS responses. We’ve incorporated the DoH data into NetworkMiner’s DNS tab, so that you can analyze it just like normal DNS traffic.

DoH traffic to mozilla.cloudflare-dns.com in NetworkMiner’s DNS tab

Image: DoH traffic to mozilla.cloudflare-dns.com in NetworkMiner’s DNS tab

Please note that NetworkMiner 2.5 does not perform TLS decryption. This means that NetworkMiner can only parse the contents of a TLS stream if it has been decrypted by a TLS proxy, such as PolarProxy.

Extracting Kerberos Hashes from PCAP

NetworkMiner’s support for the Kerberos protocol allows you to passively track which user accounts that are authenticating to what services, simply by monitoring network traffic. This is a feature is essential in order to track credential theft and lateral movement by adversaries inside your networks. After implementing kerberos username and hash extraction we realized that this feature could also be valuable for penetration testers. We therefore decided to present extracted Kerberos credentials in a format that is compatible with tools like hashcat and John the Ripper.

Kerberos krb5pa, krb5asrep and krb5tgs credentials extracted from the Wireshark sample capture file

Image: Kerberos krb5pa, krb5asrep and krb5tgs credentials extracted from the Wireshark sample capture file Krb-contrained-delegation.cap

For more information about Kerberos hashes, please see our Extracting Kerberos Credentials from PCAP blog post.

Even more NetBIOS and CIFS Artifacts!

NetworkMiner is a popular tool for extracting files transferred over SMB and SMB2 from capture files. It can also extract a great deal of information about the communicating hosts from protocols like NetBIOS and SMB/CIFS, but earlier this year Chris Raiter notified us about an important piece of information that was missing in NetworkMiner: NetBIOS Name Service (NBNS) lookups and responses!

Detection and export of NBNS packets request on twitter

A couple of months later Dan Gunter sent us another great feature request for another protocol that runs on top of NetBIOS: the CIFS Browser Protocol (aka MS-BRWS).

We’re happy to announce that NBNS queries and responses are now shown in NetworkMiner’s Parameters tab, and details like hostnames, domain names, Windows versions and uptime us extracted from the MS-BRWS protocol. See the screenshots below, which were created by loading the capture file “case09.pcap” from Richard Bejtlich’s TCP/IP Weapons School 2.0 Sample Lab into NetworkMiner 2.5. Thanks for sharing Richard!

Hostname, domain and Windows version extracted from MS-BRWS traffic

Image: Hostname, domain and Windows version extracted from MS-BRWS traffic

NBNS queries and responses in NetworkMiner’s Parameters tab

Image: NBNS queries and responses in NetworkMiner’s Parameters tab

Mono 5 Required for Linux and MacOS

Linux and MacOS users, who run NetworkMiner with help of Mono, will need to ensure they have Mono 5 (or later) installed in order to run NetworkMiner 2.5. We recommend using at least Mono 5.18.

Instructions for installing NetworkMiner on Linux can be found in our blog post ”HowTo install NetworkMiner in Ubuntu Fedora and Arch Linux”.

MacOS users can refer to our “Running NetworkMiner on Mac OS X” blog post.

Users who are unable to install Mono 5 are recommended to use the old NetworkMiner 2.4 release, which can be downloaded here: https://www.netresec.com/?download=NetworkMiner_2-4

NetworkMiner Professional

Apart from the features mentioned so far, our commercial tool NetworkMiner Professional now comes with a few additional new features. One of these features is port independent identification of RDP traffic, so that mstshash credentials can be extracted from RDP sessions even if the service doesn’t run on port 3389. The OSINT lookup context menus in NetworkMiner Professional have also been enriched with the following online services:

Several new features have also been included in the command line tool NetworkMinerCLI, including:

  • Recursive loading of PCAP files with the "-R” switch.
  • Configurable export types (hosts, files, DNS etc) with the “-x” switch.
  • Relative paths in CSV, XML and JSON/CASE exports unless the “-- absolutePaths” switch is used.

Credits

I’d like to thank Dan Gunter, Chris Raiter, Chris Sistrunk and a few more (who I cannot mention here) for contributing with feature requests and bug reports that have helped improve NetworkMiner.

Upgrading to Version 2.5

Users who have purchased a license for NetworkMiner Professional 2.x can download a free update to version 2.5 from our customer portal, or use the “Help > Check for Updates” feature. Those who instead prefer to use the free and open source version can grab the latest version of NetworkMiner from the official NetworkMiner page.

Posted by Erik Hjelmvik on Thursday, 07 November 2019 11:45:00 (UTC/GMT)

Tags: #NetworkMiner #HTTP/2 #http2 #DoH #Kerberos #NetBIOS #PCAP #hashcat #John #NetworkMinerCLI #OSINT

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Raspberry PI WiFi Access Point with TLS Inspection

This is a how-to guide for setting up a Raspberry Pi as a WiFi Access Point, which acts as a transparent TLS proxy and saves the decrypted traffic in PCAP files.

Raspberry Pi 4 Model B running PolarProxy
Image: Raspberry Pi 4 Model B running PolarProxy

Step 1: Install PolarProxy for Linux ARM

We will start with installing PolarProxy, which will be used for the TLS decryption and re-encryption. The steps are almost identical to those in the official PolarProxy installation guide, except here we will download the "linux-arm" build of PolarProxy instead of the x64 version.

sudo adduser --system --shell /bin/bash proxyuser
sudo mkdir /var/log/PolarProxy
sudo chown proxyuser:root /var/log/PolarProxy/
sudo chmod 0775 /var/log/PolarProxy/
sudo su - proxyuser
mkdir ~/PolarProxy
cd ~/PolarProxy/
curl https://www.netresec.com/?Download=PolarProxy_linux-arm | tar -xzf -
exit
sudo cp /home/proxyuser/PolarProxy/PolarProxy.service /etc/systemd/system/PolarProxy.service
sudo systemctl enable PolarProxy.service
sudo systemctl start PolarProxy.service

Note: The installation will fail on 64-bit ARM Linux OS's since we have not yet released a linux-arm64 build of PolarProxy. In the mean time, please run 32-bit ARM Linux on your Raspberry Pi proxy.

Verify that the PolarProxy service is running as expected with these commands:

systemctl status PolarProxy.service
journalctl -t PolarProxy

Step 2: Set up your Pi as a WiFi AP

The Raspberry Pi Foundation have a great guide for "Setting up a Raspberry Pi as a Wireless Access Point". Follow the instructions in their guide for the NAT mode setup (first section), but replace the iptables config with this:

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A INPUT -i wlan0 -p tcp --dport 10443 -m state --state NEW -j ACCEPT
sudo iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 443 -j REDIRECT --to 10443
Then save the iptables rules with:
sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"
Finally, edit /etc/rc.local and add this iptables-restore command just above "exit 0" to install the rules on boot.
iptables-restore < /etc/iptables.ipv4.nat

Step 3: Configure the Clients

The final step is to connect the clients (phones, tablets or computers) to the Raspberry Pi WiFi Access Point and install the root CA from PolarProxy.

Follow the instructions for "Trusting the PolarProxy root CA" in the official PolarProxy setup guide to install the public certificate from the TLS proxy in your clients. The certificate can be downloaded from the Raspberry Pi by browsing to http://192.168.4.1:10080/polarproxy.cer.

PCAP PCAP PCAP

Your Raspberry Pi WiFi AP will now intercept all HTTPS traffic going to tcp/443 and save the decrypted traffic in PCAP files, one per hour. The PCAP files with decrypted TLS traffic can be found in the /var/log/PolarProxy/ directory of your Raspberry Pi.

pi@raspberrypi:/var/log/PolarProxy $ ls *.pcap
proxy-190925-075704.pcap proxy-190925-152902.pcap
proxy-190925-085704.pcap proxy-190925-162902.pcap
proxy-190925-095704.pcap proxy-190925-172902.pcap
proxy-190925-105704.pcap proxy-190925-182902.pcap
proxy-190925-115704.pcap proxy-190926-062902.pcap
proxy-190925-125704.pcap proxy-190926-072902.pcap
proxy-190925-132704.pcap proxy-190926-082902.pcap
proxy-190925-132902.pcap proxy-190926-092902.pcap
proxy-190925-142902.pcap proxy-190926-102902.pcap

HTTP/2 traffic to Facebook opened in Wireshark
Image: Decrypted HTTP/2 traffic to Facebook opened in Wireshark

Posted by Erik Hjelmvik on Thursday, 26 September 2019 11:37:00 (UTC/GMT)

Tags: #PolarProxy #PCAP #WiFi #TLS #SSL #HTTPS #Wireshark #http2

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NETRESEC on Twitter

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book

Recommended Books

» The Practice of Network Security Monitoring, Richard Bejtlich (2013)

» Applied Network Security Monitoring, Chris Sanders and Jason Smith (2013)

» Network Forensics, Sherri Davidoff and Jonathan Ham (2012)

» The Tao of Network Security Monitoring, Richard Bejtlich (2004)

» Practical Packet Analysis, Chris Sanders (2017)

» Windows Forensic Analysis, Harlan Carvey (2009)

» TCP/IP Illustrated, Volume 1, Kevin Fall and Richard Stevens (2011)

» Industrial Network Security, Eric D. Knapp and Joel Langill (2014)