Raspberry Robin worm part of larger ecosystem facilitating pre-ransomware activity

 Here is a post from Microsoft that I feel you should know about

Microsoft has discovered recent activity indicating that the Raspberry Robin worm is part of a complex and interconnected malware ecosystem, with links to other malware families and alternate infection methods beyond its original USB drive spread. These infections lead to follow-on hands-on-keyboard attacks and human-operated ransomware activity. Our continuous tracking of Raspberry Robin-related activity also shows a very active operation: Microsoft Defender for Endpoint data indicates that nearly 3,000 devices in almost 1,000 organizations have seen at least one Raspberry Robin payload-related alert in the last 30 days.

Raspberry Robin has evolved from being a widely distributed worm with no observed post-infection actions when Red Canary first reported it in May 2022, to one of the largest malware distribution platforms currently active. In July 2022, Microsoft security researchers observed devices infected with Raspberry Robin being installed with the FakeUpdates malware, which led to DEV-0243 activity. DEV-0243, a ransomware-associated activity group that overlaps with actions tracked as EvilCorp by other vendors, was first observed deploying the LockBit ransomware as a service (RaaS) payload in November 2021. Since then, Raspberry Robin has also started deploying IcedID, Bumblebee, and Truebot based on our investigations.

In October 2022, Microsoft observed Raspberry Robin being used in post-compromise activity attributed to another actor, DEV-0950 (which overlaps with groups tracked publicly as FIN11/TA505). From a Raspberry Robin infection, the DEV-0950 activity led to Cobalt Strike hands-on-keyboard compromises, sometimes with a Truebot infection observed in between the Raspberry Robin and Cobalt Strike stage. The activity culminated in deployments of the Clop ransomware. DEV-0950 traditionally uses phishing to acquire the majority of their victims, so this notable shift to using Raspberry Robin enables them to deliver payloads to existing infections and move their campaigns more quickly to ransomware stages.

Given the interconnected nature of the cybercriminal economy, it’s possible that the actors behind these Raspberry Robin-related malware campaigns—usually distributed through other means like malicious ads or email—are paying the Raspberry Robin operators for malware installs.

Raspberry Robin attacks involve multi-stage intrusions, and its post-compromise activities require access to highly privileged credentials to cause widespread impact. Organizations can defend their networks from this threat by having security solutions like Microsoft Defender for Endpoint and Microsoft Defender Antivirus, which is built into Windows, to help detect Raspberry Robin and its follow-on activities, and by applying best practices related to credential hygiene, network segmentation, and attack surface reduction.

In this blog, we share our detailed analysis of these attacks and shed light on Raspberry Robin’s origins, since its earliest identified activity in September 2021, and motivations which have been debated since it was first reported in May 2022. We also provide mitigation guidance and other recommendations defenders can use to limit this malware’s spread and impact from follow-on hands-on-keyboard attacks.

A new worm hatches: Raspberry Robin’s initial propagation via USB drives

In early May 2022, Red Canary reported that a new worm named Raspberry Robin was spreading to Windows systems through infected USB drives. The USB drive contains a Windows shortcut (LNK) file disguised as a folder. In earlier infections, this file used a generic file name like recovery.lnk, but in more recent ones, it uses brands of USB drives. It should be noted that USB-worming malware isn’t new, and many organizations no longer track these as a top threat.  

For an attack relying on a USB drive to run malware upon insertion, the targeted system’s autorun.inf must be edited or configured to specify which code to start when the drive is plugged in. Autorun of removable media is disabled on Windows by default. However, many organizations have widely enabled it through legacy Group Policy changes.

There has been much public debate about whether the Raspberry Robin drives use autoruns to launch or if it relies purely on social engineering to encourage users to click the LNK file. Microsoft Threat Intelligence Center (MSTIC) and Microsoft Detection and Response Team (DART) research has confirmed that both instances exist in observed attacks. Some Raspberry Robin drives only have the LNK and executable files, while drives from earlier infections have a configured autorun.inf. This change could be linked to why the names of the shortcut files changed from more generic names to brand names of USB drives, possibly encouraging a user to execute the LNK file.

Upon insertion of the infected drive or launching of the LNK file, the UserAssist registry key in Windows—where Windows Explorer maintains a list of launched programs—is updated with a new value indicating a program was launched by Windows. 

This diagram shows the linear progression of earlier Raspberry Robin infections.
Figure 1. Attack chain of the original Raspberry Robin infections

The UserAssist key stores the names of launched programs in ROT13-ciphered format, which means that every letter in the name of the program is replaced with the 13th letter in the alphabet after it. This routine makes the entries in this registry key not immediately readable. The UserAssist key is a useful forensic artifact to demonstrate which applications were launched on Windows, as outlined in Red Canary’s blog.

Windows shortcut files are mostly used to create an easy-to-find shortcut to launch a program, such as pinning a link to a user’s browser on the taskbar. However, the format allows the launching of any code, and attackers often use LNK files to launch malicious scripts or run stored code remotely. Raspberry Robin’s LNK file points to cmd.exe to launch the Windows Installer service msiexec.exe and install a malicious payload hosted on compromised QNAP network attached storage (NAS) devices.

Screenshot of command lines where Raspberry Robin uses the Windows installer service to connect to an external domain.
Figure 2. Examples of URLs connecting to an external domain

Once the Raspberry Robin payload is running, it spawns additional processes by using system binaries such as rundll32.exeodbcconf.exe, and control.exe to use as living-off-the-land binaries (LOLBins) to run malicious code. Raspberry Robin also launches code via fodhelper.exe, a system binary for managing optional features, as a user access control (UAC) bypass.

The malware injects into system processes including regsvr32.exerundll32.exe, and dllhost.exe and connects to various command-and-control (C2) servers hosted on Tor nodes.

In most instances, Raspberry Robin persists by adding itself to the RunOnce key of the registry hive associated with the user who executed the initial malware install. The registry key points to the Raspberry Robin binary, which has a random name and a random extension such as .mh or .vdm in the user’s AppData folder or to ProgramData. The key uses the intended purpose of regsvr32.exe to launch the portable executable (PE) file, allowing the randomized non-standard file extension to launch the executable content. 

Screenshot of the contents of the RunOnce registry key where the value points to the randomly-named Raspberry Robin file.
Figure 3. Example of the contents of the RunOnce key

Entries in the RunOnce key delete the registry entry prior to launching the executable content at sign-in. Raspberry Robin re-adds this key once it is successfully running to ensure persistence. After the initial infection, this leads to RunOnce.exe launching the malware payload in timelines. Raspberry Robin also temporarily renames the RunOnce key when writing to it to evade detections.

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