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TRU Positives: Weekly investigation summaries and recommendations from eSentire's Threat Response Unit (TRU)
BY eSentire Threat Response Unit (TRU)
February 10, 2023 | 8 MINS READ
Adversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters and Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.
We have discovered some of the most dangerous threats and nation state attacks in our space – including the Kaseya MSP breach and the more_eggs malware.
Our Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced Threat Analytics driven by our Threat Response Unit – the TRU team.
In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.
Here’s the latest from our TRU Team…
Since January 31st, 2023, TRU has observed a noted increase in malware delivery using OneNote documents. This follows reports dating back to December 2022 of OneNote documents being used to deliver Formbook malware.
OneNote documents have been adopted to deliver AsyncRAT, Redline Stealer, QuasarRAT, Bumblebee and Qakbot malware. The latter three have been observed in our telemetry and the majority of observations were tied to Qakbot.
As explained by Didier Stevens in his recent InfoSec Handler Diary, OneNote documents use a binary format called MS-ONESTORE. Executable files can be embedded within these documents then launched by clicking an icon on the page (Figure 1). “Weaponizing” OneNote documents is as straightforward as inserting executable files (including scripts) into the document body.
Clicking the icon would result in a popup warning that opening the attachment could result in harm (Figure 2). If ignored, OneNote will spawn the appropriate child process (e.g., PowerShell) to execute the code. The popup does not provide any specific contextual information to help the user decide on whether the attachment is safe.
Like other warnings of this nature, it recommends the user judge the risk based on the source of the attachment. This behavior has been long exploited by the likes of Qakbot or Emotet using stolen email threads to masquerade as a trusted source.
In addition to easy insertion of clickable executable content, OneNote offers another desirable trait for malware execution as the attachment can still be clicked even when hidden behind an image (Figure 3).
The image below offers an example of a typical malicious OneNote document. In our observations, these documents masquerade as either OneNote or Office365 with text that lures the victim into clicking on an icon containing the payload (Figure 4).
In the above sample, clicking the icon and accepting the warning prompt would execute an embedded HTA file using the MSHTA process (Figure 5). This HTA file used Curl to retrieve then execute a Qakbot DLL on the machine.
Examining endpoint telemetry shows this execution chain in detail:
In this particular example, Qakbot injected into wermgr.exe then spawned various Windows binaries to orient and assess the value of the target for further exploitation (Figure 7).
In early February, TRU analyzed a Bumblebee sample intercepted by our MDR for Endpoint service. The execution was blocked, but analysis tied it to an invoice themed email containing a OneNote attachment (Figure 8).
The attachment used the typical OneNote theme to lure the victim in clicking on the “Open” image (Figure 9). This launched the “Open.hta” HTML application file which was blocked by MDR for Endpoint.
Recently observed Qakbot samples in our telemetry employed an embedded PowerShell script using a generic OneNote theme and executed by double clicking the “Open” icon and ignoring the content warning (Figure 11).
We have also seen recent versions with lightly obfuscated PowerShell code (Figure 12). The lack of robust obfuscation may speak to benefits of the OneNote filetype in evading content inspection filters currently.
Finally, as explained by a TRU researcher on Twitter, QuasarRAT was observed in early February using OneNote documents. This sample contained an embedded CAB file which dropped and executed a VBS script payload (Figure 13). The VBS script called PowerShell to retrieve a PS script from a remote host. The final payload was a .NET executable that contained Quasar RAT.
Fortunately, detecting malicious OneNote document execution is relatively straightforward.
In this case, our team of 24/7 SOC Cyber Analysts and Threat Response Unit (TRU) used MDR for Endpoint rules to look for onenote.exe spawning executables or scripts. Existing signatures for Qakbot and other malware abusing this technique were successful in detecting this activity.
As the adversarial TTPs grow in sophistication, they lead to a certain level of difficulty at which critical business decisions must be made. Preventing the various attack paths utilized by modern threat actors requires actively monitoring the threat landscape, developing, and deploying endpoint detection, and the ability to investigate logs & network data during active intrusions.
To increase your resilience against cyber threats like this, we recommend:
|OneNote Payload Locations
eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.
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The eSentire Threat Response Unit (TRU) is an industry-leading threat research team committed to helping your organization become more resilient. TRU is an elite team of threat hunters and researchers that supports our 24/7 Security Operations Centers (SOCs), builds threat detection models across the eSentire XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. By providing complete visibility across your attack surface and performing global threat sweeps and proactive hypothesis-driven threat hunts augmented by original threat research, we are laser-focused on defending your organization against known and unknown threats.