Are you interested in learning more about how to analyze network traffic from Cobalt Strike and other backdoors, malware and hacker tools? Then take a look at our upcoming network forensics classes!
Posted by Erik Hjelmvik on Thursday, 04 January 2024 10:12:00 (UTC/GMT)
In this video I look for C2 traffic by doing something I call Rinse-Repeat Threat Hunting,
which is a method for removing "normal" traffic in order to look closer at what isn't normal.
The video was recorded in a Windows Sandbox in order to avoid accidentally infecting my Windows PC with malware.
In this video I demonstrate that text typed into the Windows 10 start menu gets sent to Microsoft and how
that traffic can be intercepted, decrypted and parsed.
What Was Sent?
The XML files shown in the video were sent by Cortana's "SmartSearch" app to https://www.bing.com/threshold/xls.aspx in HTTP/2 POST requests.
As shown in the video, the POST'ed keystrokes can be found inside requestInfo XML tags that have a "RawQuery" key.
The following tcpdump and grep commands can be used to list the RawQuery data sent to Bing in these HTTP/2 requests:
tcpdump -A -r proxy-210927-134557.pcap | grep -a -o 'key="RawQuery" value="[^"]*"'
Running that command on the PolarProxy PCAP file from the video gives the following output:
The same data also gets sent in the query string variable "qry" of GET requests for
https://www.bing.com/AS/API/WindowsCortanaPane/V2/Suggestions, as shown in this NetworkMiner screenshot.
Image: NetworkMiner's Parameters tab with filter "qry" on "Parameter name" column
How to Intercept, Decrypt and Decode HTTPS Traffic
The following section presents the technical details regarding my setup,
so that others can reproduce and verify these findings.
My first step was to install PolarProxy on a Linux machine on the local network.
PolarProxy is a TLS proxy, which can intercept and decrypt TLS traffic.
This TLS proxy is primarily designed to decrypt traffic from malware and hackers,
but can also be used to decrypt legitimate traffic when needed.
PolarProxy was configured to listen for incoming TLS connections on TCP port 443
and output PCAP data with the decrypted traffic as if it had been transmitted over TCP 80.
The decrypted traffic was accessible as a real-time stream through a
PCAP-over-IP service running on port 57012.
Here's the full command that was used to start PolarProxy:
In the video I showed the Windows 10 client's modified hosts file, which included an entry for www.bing.com pointing to the PolarProxy machine.
What was not shown in the video though, is that PolarProxy's own CA certificate had been added to the Win10 machine's list of trusted root CA's,
as explained in the "Trusting the PolarProxy root CA" section of the PolarProxy installation instructions.
With these two changes in place all HTTPS requests for www.bing.com from the Win10 PC got diverted through the PolarProxy TLS inspection service,
which then decrypted and re-encrypted the traffic before forwarding it to Bing.
The decrypted Bing requests could be accessed either locally on the Linux machine,
or remotely using the PCAP-over-IP service on TCP port 57012.
I used NetworkMiner to read the live PCAP stream with decrypted traffic from port 57012 and extract all files being sent and received in real-time.
As part of delivering Windows 10 as a service, updates may be delivered to provide ongoing new features to Bing search, such as new visual layouts, styles and search code.
No query or search usage data is sent to Microsoft, in accordance with the customer's chosen privacy settings.
There are plenty of how-to guides online with instructions on how the Cortana search feature can be disabled.
Most of these guides suggest disabling the AllowCortana setting in group policies or in the registry.
We've tried several of the settings suggested in these how-to guides, but none of them seem to prevent Windows from sending keystrokes to Bing.
If you know how to successfully disable Cortana's Bing searches,
then please feel free to reach out to us so that we can update this blog post.
UPDATE 210928 - How to Actually Disable Cortana Search
Twitter user @GeorgeProfonde3 reached out
to suggest a fix that might prevent the start menu from sending data to Bing.
We have now verified this fix and we're happy to announce that it works (at least for us).
Start regedit.exe
Open the following registry key: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Search
Ensure that the value for CortanaConsent is set to 0
Create a new DWORD registry entry called "BingSearchEnabled" with value 0
You should no longer see any connections to www.bing.com when interacting with the start menu after implementing this fix.
UPDATE 211015 - Another way to Disable Cortana Search
You may need to use a different method to disable the start meny search, depending on your Windows version and build.
Kimberly (@StopMalvertisin) suggested the following method, which seems to work on Windows 11:
Start regedit.exe
Create a registry key for: HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Windows\Explorer
Create a new DWORD registry entry called "DisableSearchBoxSuggestions" with value 1
Disabling Start Menu Search from Group Policy
There are also a few different methods for disabling start menu searches using GPO.
However, please note that your success will vary depending on your Windows version and build.
GPO Method #1
Start gpedit.msc
Open the following branch: User configuration\Administrative templates\Windows components\File Explorer
Enable the following group policy:
"Turn off display of recent search entries in the File Explorer search box"
GPO Method #2
Start gpedit.msc
Open the following branch: User Configuration\Administrative Templates\Start Menu and Taskbar
Enable the following group policy:
"Do not search communications"
Posted by Erik Hjelmvik on Tuesday, 28 September 2021 08:24:00 (UTC/GMT)
I recently came across a fantastic digital forensics dataset at dfirmadness.com,
which was created by James Smith.
There is a case called The Stolen Szechuan Sauce
on this website that includes forensic artifacts like disk images, memory dumps and a PCAP file (well, pcap-ng actually).
In this video I demonstrate how I analyzed the capture file case001.pcap from this case.
Follow Along in the Analysis
Please feel free to follow along in the analysis performed in the video.
You should be able to use the free trial version of CapLoader
and the free open source version of NetworkMiner
to perform most of the tasks I did in the video.
Here are some of the BPF and Column Criteria filters that I used in the video, so that you can copy/paste them into CapLoader.
net 10.0.0.0/8
Umbrella_Domain =
not ip6 and not net 224.0.0.0/4
host 194.61.24.102 or host 203.78.103.109 or port 3389
This video shows how Cobalt Strike and Hancitor C2 traffic can be detected using CapLoader.
I bet you’re going:
😱 OMG he’s analyzing Windows malware on a Windows PC!!!
Relax, I know what I’m doing. I have also taken the precaution of analyzing the PCAP file in a
Windows Sandbox, which just takes a couple of seconds to deploy and run.
CapLoader’s Services tab shows us that the connections to TCP 80 and 443 on 103.207.42.11 are very periodic, with a detected period of exactly 1 minute.
CapLoader successfully identifies the protocols for these two services as Cobalt Strike over HTTP and Cobalt Strike over SSL, respectively.
The third service in this list is also very periodic, that’s the Hancitor trojan beaconing to its C2 server every two minutes.
CapLoader uses machine learning to identify the application layer protocol based on the behavior of the traffic, not the port number.
This means that there can be false positives, i.e. the protocol classification that CapLoader gives a flow or service might be wrong.
It is more common, however, for CapLoader to yield false negatives, which means that it can't identify the protocol.
The detection of Cobalt Strike inside of HTTP and SSL traffic was recently introduced in the latest
1.9 release of CapLoader.
I expected this feature to detect Cobalt Strike traffic in HTTP, but I was delighted to see that CapLoader often detects even TLS encrypted Cobalt Strike beaconing with really good precision!
As shown in the video, the Cobalt Strike beacon config can easily be extracted from the network traffic using
NetworkMiner and Didier Stevens’
1768 K python script.
The output from Didier’s 7868.py tool looks something like this:
As you can see, it uses HTTP for transport with a “sleeptime” of 1 minute (60000 ms) and 0% jitter.
This means that a new connection will be made to the Cobalt Strike C2 server every minute.
The fact that there was no jitter is what gives this service such a high value in CapLoader’s “Periodicity” column.
Network Forensics Training
Are you interested in learning more about how to analyze network traffic from Cobalt Strike and other backdoors, malware and hacker tools?
Then take a look at the live online network forensics classes I will be teaching in September and October!
Posted by Erik Hjelmvik on Monday, 31 May 2021 08:30:00 (UTC/GMT)
This video tutorial is a walkthrough of how you can analyze the PCAP file
UISGCON-traffic-analysis-task-pcap-2-of-2.pcap
(created by Brad Duncan).
The capture file contains a malicious Word Document (macro downloader), Emotet (banking trojan),
TrickBot/Trickster (banking trojan) and an EternalChampion (CVE-2017-0146)
exploit used to perform lateral movement.
Wanna improve your network forensics skills? Take a look at our
trainings,
the next scheduled class is on March 18-19 at the
TROOPERS conference in Germany.
Posted by Erik Hjelmvik on Wednesday, 23 January 2019 14:00:00 (UTC/GMT)
This short video demonstrates how you can search through PCAP files with regular expressions (regex) using
CapLoader and how this can be leveraged in order to
improve IDS signatures.
The EmergingThreats snort/suricata rule mentioned in the video is
SID 2014411
“ET TROJAN Fareit/Pony Downloader Checkin 2”.
The header accept-encoding header with quality factor 0 used by the Pony malware is: Accept-Encoding: identity, *;q=0
And here is the regular expression used to search for that exact header:
\r\nAccept-Encoding: identity, \*;q=0\r\n
After recording the video I noticed that the leaked source code for Pony 2.0 actually contains this accept-encoding header as a
hard-coded string. Have a look in the
redirect.php file, where they set
curl’s CURLOPT_HTTPHEADER to this specific string.
Wanna learn more about the intended use of quality factors in HTTP accept headers?
Then have a look at section 14.1 of RFC 2616section 5.3.4 of RFC 7231, which defines how to use qvalues (i.e. quality factors) in the Accept-Encoding header.
This network forensics video tutorial covers analysis of a malware redirect chain, where a PC is infected through the RIG Exploit Kit.
A PCAP file, from Brad Duncan'smalware-traffic-analysis.net website,
is opened in NetworkMiner Professional in order to follow a redirect chain via a couple of hacked websites before delivering malware to the PC.
