NETRESEC Network Security Blog


CapLoader 1.6 Released

CapLoader 1.6

CapLoader is designed to simplify complex tasks, such as digging through gigabytes of PCAP data looking for traffic that sticks out or shouldn’t be there. Improved usability has therefore been the primary goal, when developing CapLoader 1.6, in order to help our users do their work even more efficiently than before.

Some of the new features in CapLoader 1.6 are:

  • Context aware selection and filter suggestions when right-clicking a flow, session or host.
  • Support for IPv6 addresses in the BPF syntax for Input Filter as well as Display Filter.
  • Flows that are inactive for more than 60 minutes are considered closed. This timeout is configurable in Tools > Settings.


Latency Measurements

CapLoader 1.6 also introduces a new column in the Flows tab labeled “Initial_RTT”, which shows the Round Trip Time (RTT) measured during the start of a session. The RTT is defined as “the time it takes for a signal to be sent plus the time it takes for an acknowledgment of that signal to be received”. RTT is often called “ping time” because the ping utility computes the RTT by sending ICMP echo requests and measuring the delay until a reply is received.

Initial RTT in CapLoader Flows Tab
Image: CapLoader 1.6 showing ICMP and TCP round trip times.

But using a PCAP file to measure the RTT between two hosts isn’t as straight forward as one might think. One complicating factor is that the PCAP might be generated by the client, server or by any device in between. If we know that the sniffing point is at the client then things are simple, because we can then use the delta-time between an ICMP echo request and the returning ICMP echo response as RTT. In lack of ping traffic the same thing can be achieved with TCP by measuring the time between a SYN and the returning SYN+ACK packet. However, consider the situation when the sniffer is located somewhere between the client and server. The previously mentioned method would then ignore the latency between the client and sniffer, the delta-time will therefore only show the RTT between the sniffer and the server.

This problem is best solved by calculating the Initial RTT (iRTT) as the delta-time between the SYN packet and the final ACK packet in a TCP three-way handshake, as shown here:

Initial Round Trip Time in PCAP Explained
Image: Initial RTT is the total time of the black/bold packet traversal paths.

Jasper Bongertz does a great job of explaining why and how to use the iRTT in his blog post “Determining TCP Initial Round Trip Time”, so I will not cover it in any more detail here. However, keep in mind that iRTT can only be calculated this way for TCP sessions. CapLoader therefore falls back on measuring the delta time between the first packet in each direction when it comes to transport protocols like UDP and ICMP.


Exclusive Features Not Available in the Free Trail

The new features mentioned so far are all available in the free 30 day CapLoader trial, which can be downloaded from our CapLoader product page (no registration required). But we’ve also added features that are only available in the commercial/professional edition of CapLoader. One such exclusive feature is the matching of hostnames against the Cisco Umbrella top 1 million domain list. CapLoader already had a feature for matching domain names against the Alexa top 1 million list, so the addition of the Umbrella list might seem redundant. But it’s actually not, the two lists are compiled using different data sources and therefore complement each other (see our blog post “Domain Whitelist Benchmark: Alexa vs Umbrella” for more details). Also, the Umbrella list contains subdomains (such as www.google.com, safebrowsing.google.com and accounts.google.com) while the Alexa list only contains main domains (like “google.com”). CapLoader can therefore do more fine-granular domain matching with the Umbrella list (requiring a full match of the Umbrella domain), while the Alexa list enables a more rough “catch ‘em all” approach (allowing *.google.com to be matched).

CapLoader Hosts tab with ASN, Alexa and Umbrella details

CapLoader 1.6 also comes with an ASN lookup feature, which presents the autonomous system number (ASN) and organization name for IPv4 and IPv6 addresses in a PCAP file (see image above). The ASN lookup is built using the GeoLite database created by MaxMind. The information gained from the MaxMind ASN database is also used to provide intelligent display filter CIDR suggestions in the context menu that pops up when right-clicking a flow, service or host.

CapLoader Flows tab with context menu for Apply as Display Filter
Image: Context menu suggests Display Filter BPF “net 104.84.152.0/17” based on the server IP in the right-clicked flow.

Users who have previously purchased a license for CapLoader can download a free update to version 1.6 from our customer portal.


Credits and T-shirts

We’d like to thank Christian Reusch for suggesting the Initial RTT feature and Daan from the Dutch Ministry of Defence for suggesting the ASN lookup feature. We’d also like to thank David Billa, Ran Tohar Braun and Stephen Bell for discovering and reporting bugs in CapLoader which now have been fixed. These three guys have received a “PCAP or it didn’t happen” t-shirt as promised in our Bug Bounty Program.

Got a t-shirt for crashing CapLoader

If you too wanna express your view of outlandish cyber attack claims without evidence, then please feel free to send us your bug reports and get rewarded with a “PCAP or it didn’t happen” t-shirt!

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Posted by Erik Hjelmvik on Monday, 09 October 2017 08:12:00 (UTC/GMT)


Hunting AdwindRAT with SSL Heuristics

An increasing number of malware families employ SSL/TLS encryption in order to evade detection by Network Intrusion Detection Systems (NIDS). In this blog post I’m gonna have a look at Adwind, which is a cross-platform Remote Access Trojan (RAT) that has been using SSL to conceal it’s traffic for several years. AdwindRAT typically connects SSL sessions to seemingly random TCP ports on the C2 servers. Hence, a heuristic that could potentially be used to hunt for Adwind RAT malware is to look for SSL traffic going to TCP ports that normally don’t use SSL. However, relying on ONLY that heuristic would generate way too many false positives.

Brad Duncan did an interesting writeup about Adwind RAT back in 2015, where he wrote:

I saw the same certificate information used last week, and it continues this week.
  • commonName = assylias
  • organizationName = assylias.Inc
  • countryName = FR
Currently, this may be the best way to identify Adwind-based post-infection traffic. Look for SSL traffic on a non-standard TCP port using that particular certificate.

Unfortunately, Adwind RAT has evolved to use other CN’s in their new certificates, so looking for “assylias.Inc” will not cut it anymore. However, looking for SSL traffic on non-standard TCP ports still holds on the latest Adwind RAT samples that we’ve analyzed.

The PT Research Attack Detection Team (ADT) sent an email with IDS signatures for detecting AdwindRAT to the Emerging-Sigs mailing list a few days ago, where they wrote:

“We offer one of the ways to detect malicious AdwindRAT software inside the encrypted traffic. Recently, the detection of this malicious program in network traffic is significantly reduced due to encryption. As a result of the research, a stable structure of data fragments was created.”

Not only is it awesome that they were able to detect static patterns in the encrypted data, they also provided 25 PCAP files containing AdwindRAT traffic. I loaded these PCAP files into NetworkMiner Professional in order to have a look at the X.509 certificates. NetworkMiner Professional supports Port-Independent Protocol Identification (PIPI), which means that it will automatically identify the C2 sessions as SSL, regardless of which port that is used. It will also automatically extract the X.509 certificates along with any other parameters that can be extracted from the SSL handshake before the session goes encrypted.

X.509 certificates extracted from AdwindRAT PCAP by NetworkMiner Image: Files extracted from ADT’s PCAP files that mach “Oracle” and “cer”.

In this recent campaign the attackers used X.509 certificates claiming to be from Oracle. The majory of the extracted certificates were exactly 1237 bytes long, so maybe they’re all identical? This is what the first extracted X.509 certificate looks like:

Self-signed Oracle America, Inc. X.509 certificate

The cert claims to be valid for a whopping 100 years!

Self-signed Oracle America, Inc. X.509 certificate

Self-signed, not trusted.

However, after opening a few of the other certificates it's clear that each C2 server is using a unique X.509 certificate. This can be quickly confirmed by opening the parameters tab in NetworkMiner Pro and showing only the Certificate Hash or Subject Key Identifier values.

NetworkMiner Parameters tab showing Certificate Hash values Image: Certificate Hash values found in Adwind RAT’s SSL traffic

I also noted that the CN of the certificates isn’t constant either; these samples use CN’s such as “Oracle America”, “Oracle Tanzania”, “Oracle Arusha Inc.”, “Oracle Leonardo” and “Oracle Heaven”.

The CN field is normally used to specify which domain(s) the certificate is valid for, together with any additinoal Subject Alternative Name field. However, Adwind RAT’s certificates don’t contain any domain name in the CN field and they don’t have an Alternative Name record. This might very well change in future versions of this piece of malware though, but I don’t expect the malware authors to generate a certificate with a CN matching the domain name used by each C2 server. I can therefore use this assumption in order to better hunt for Adwind RAT traffic.

But how do I know what public domain name the C2 server has? One solution is to use passive DNS, i.e. to capture all DNS traffic in order to do passive lookups locally. Another solution is to leverage the fact that the Adwind RAT clients use the Server Name Indication (SNI) when connecting to the C2 servers.

TLS Server Name (aka SNI) and Subject CN values don’t match for AdwindRAT Image: TLS Server Name (aka SNI) and Subject CN values don’t match for AdwindRAT

TLS Server Name (SNI) with matching Subject CN from Google Image: TLS Server Name (SNI) with matching Subject CN from Google.

My conclusion is therefore that Brad’s recommendations from 2015 are still pretty okay, even for the latest wave of Adwind RAT traffic. However, instead of looking for a fix CN string I’d prefer to use the following heuristics to hunt for this type of C2 traffic:

  • SSL traffic to non-standard SSL port
  • Self signed X.509 certificate
  • The SNI domain name in the Client Hello message does not match the CN or Subject Alternative Name of the certificate.

These heuristics will match more than just Adwind RAT traffic though. You’ll find that the exact same heuristics will also help identify other pieces of SSL-enabled malware as well as Tor traffic.

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Posted by Erik Hjelmvik on Monday, 04 September 2017 19:01:00 (UTC/GMT)


NetworkMiner 2.2 Released

NetworkMiner 2.2 = Harder Better Faster Stronger

NetworkMiner 2.2 is faster, better and stronger than ever before! The PCAP parsing speed has more than doubled and even more details are now extracted from analyzed packet capture files.

The improved parsing speed of NetworkMiner 2.2 can be enjoyed regardless if NetworkMiner is run in Windows or Linux, additionally the user interface is more responsive and flickers way less when capture files are being loaded.

User Interface Improvements

The keyword filter available in the Files, Messages, Sessions, DNS and Parameters tabs has been improved so that the rows now can be filtered on a single column of choice by selecting the desired column in a drop-down list. There is also an “Any column” option, which can be used to search for the keyword in all columns.

Keyword drop-down in NetworkMiner's Parameters tab

The Messages tab has also received an additional feature, which allows the filter keyword to be matched against the text in the message body as well as email headers when the “Any column” option is selected. This allows for an efficient analysis of messages (such as emails sent/received through SMTP, POP3 and IMAP as well as IRC messages and some HTTP based messaging platforms), since the messages can be filtered just like in a normal e-mail client.

We have also given up on using local timestamp formats; timestamps are now instead shown using the yyyy-MM-dd HH:mm:ss format with time zone explicitly stated.

Protocol Parsers

NetworkMiner 2.2 comes with a parser for the Remote Desktop Protocol (RDP), which rides on top of COTP and TPKT. The RDP parser is primarily used in order to extract usernames from RDP cookies and show them on the Credentials tab. This new version also comes with better extraction of SMB1 and SMB2 details, such as NTLM SSP usernames.

RDP Cookies extracted with NetworkMiner 2.2

One big change that has been made behind the scenes of NetworkMiner is the move from .NET Framework 2.0 to version 4.0. This move doesn’t require any special measures to be taken for most Microsoft Windows users since the 4.0 Framework is typically already installed on these machines. If you’re running NetworkMiner in Linux, however, you might wanna check out our updated blog post on how to install NetworkMiner in Linux.

We have also added an automatic check for new versions of NetworkMiner, which runs every time the tool is started. This update check can be disabled by adding a --noupdatecheck switch to the command line when starting NetworkMiner.

NetworkMiner.exe --noupdatecheck capturefile.pcap

NetworkMiner Professional

Even though NetworkMiner 2.2 now uses ISO-like time representations NetworkMiner still has to decide which time zone to use for the timestamps. The default decision has always been to use the same time zone as the local machine, but NetworkMiner Professional now additionally comes with an option that allows the user to select whether to use UTC (as nature intended), the local time zone or some other custom time zone for displaying timestamps. The time zone setting can be found in the “Tools > Settings” menu.

The Port-Independent-Protocol-Detection (PIPI) feature in NetworkMiner Pro has been improved for more reliable identification of HTTP, SSH, SOCKS, FTP and SSL sessions running on non-standard port numbers.

CASE / JSON-LD Export

We are happy to announce that the professional edition of NetworkMiner 2.2 now has support for exporting extracted details using the Cyber-investigation Analysis Standard Expression (CASE) format, which is a JSON-LD format for digital forensics data. The CASE export is also available in the command line tool NetworkMinerCLI.

We would like to thank Europol for recommending us to implement the CASE export format in their effort to adopt CASE as a standard digital forensic format. Several other companies in the digital forensics field are currently looking into implementing CASE in their tools, including AccessData, Cellebrite, Guidance, Volatility and XRY. We believe the CASE format will become a popular format for exchanging digital forensic data between tools for digital forensics, log correlation and SIEM solutions.

We will, however, still continue supporting and maintaining the CSV and XML export formats in NetworkMiner Professional and NetworkMinerCLI alongside the new CASE format.

Credits

I would like to thank Sebastian Gebhard and Clinton Page for reporting bugs in the Credentials tab and TFTP parsing code that now have been fixed. I would also like to thank Jeff Carrell for providing a capture file that has been used to debug an issue in NetworkMiner’s OpenFlow parser. There are also a couple of users who have suggested new features that have made it into this release of NetworkMiner. Marc Lindike suggested the powerful deep search of extracted messages and Niclas Hirschfeld proposed a new option in the PCAP-over-IP functionality that allows NetworkMiner to receive PCAP data via a remote netcat listener.

Upgrading to Version 2.2

Users who have purchased a license for NetworkMiner Professional 2.x can download a free update to version 2.2 from our customer portal.

Those who instead prefer to use the free and open source version can grab the latest version of NetworkMiner from the official NetworkMiner page.

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Posted by Erik Hjelmvik on Tuesday, 22 August 2017 11:37:00 (UTC/GMT)

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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)