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QakBot Takedown Payload Evaluation –

QakBot Takedown Payload Evaluation –

2023-09-01 14:45:15

In a latest worldwide operation, regulation enforcement businesses from the US and EU have taken down the QakBot botnet (see Press Release by U.S. Department of Justice, or in German, Press Release by Bundeskriminalamt).

QakBot is a infamous malware that was primarily distributed through malicious emails. Its principal goal was to achieve preliminary entry to a community. As soon as a foothold had been established and the sufferer regarded like a promising goal, the botnet operators will present (or extra doubtless, promote) the entry to a ransomware group. The ransomware group will attempt to increase their attain within the sufferer’s community and in the end deploy a ransomware payload with a purpose to extort cash from the sufferer.

Different performance included a plugin system that may very well be used to increase the malware’s capabilities – e.g., an Outlook stealer that exfiltrates emails and tackle books with a purpose to determine new targets for e-mail spam or to make the emails look extra convincing. Moreover, there was a worm plugin that mechanically enumerated the community and tried to entry different machines utilizing weak credentials and tried to unfold the an infection there utilizing a mix of SMB (Server Message Block, aka “Home windows filesharing”) and Service Management Supervisor entry through RPC (Distant Process Name).

G DATA Superior Analytics has been monitoring the QakBot botnet in order that we obtain new bot variations and plugins as early as doable. Late on August twenty fifth, the C2 servers began distributing a payload utilizing command kind 42, which executes a chunk of x86 shellcode within the context of the malware course of. The shellcode consists of two components: a ~2.5K dynamic library mapper, adopted by the library to be loaded (~11K). The library is encrypted utilizing a XOR scheme involving a 128-bit key and the present buffer offset, which is subtracted after the XOR operation. After decrypting the DLL, we get hold of a well-formed PE compiled on August sixteenth utilizing Visible Studio 2019. The next screenshot exhibits the pseudocode for the decryption:

Decryption code in shellcode

As can already be guessed from the file dimension, the DLL incorporates only a few capabilities. Because it seems, it implements the naked minimal of performance required to cease an lively occasion of QakBot on a system. The next screenshot exhibits a listing of user-defined capabilities within the DLL (whereas every part starting from __security_check_cookie belongs to the C runtime):

Features contained within the DLL

QakBot makes use of the Mersenne Tornado pseudo-random quantity generator (additionally referred to as MTRand) with a purpose to generate numerous identifiers that it’s going to use on the system. This is applicable to a large number of various objects, together with mutexes, registry key names, file names and pipe names. The generator is seeded with a CRC32 checksum derived from the pc title, quantity serial variety of the C: partition, and username. This enables the malware to persistently discover its sources throughout course of boundaries and reboots, so long as they execute underneath the identical person. As a consequence, there’s additionally no particular path the place QakBot shops itself for persistence that may be legitimate for all contaminated methods, since each the folder title (underneath %APPDATA%) and file title are generated utilizing the described mechanism.

The uninstall library constructs the title for a named pipe that the principle QakBot core polls. It connects to the pipe and easily sends a command that tells QakBot to terminate itself. The precise particulars of how this appears, together with data from a QakBot construct with debug logging, might be present in a weblog submit by SecureWorks.

One would possibly marvel how it’s doable that this cleans the an infection in a method that it received’t merely reassert itself after the following system boot. It’s because QakBot removes each its Run key from the registry and file on disk upon startup with a purpose to make the an infection tougher to detect. The termination process referred to as through pipe doesn’t restore this persistence, because it was in all probability meant for bot updates the place a more recent occasion of QakBot has spun up and is asking the previous occasion to stop.

Upon nearer inspection, we see two minor issues with the payload the place it runs into edge instances:

See Also

  1. It’s linked dynamically moderately than statically, that means it depends upon the Visible C++ 2015-2019 x86 Runtime being put in on the system. Particularly on older Home windows 7/8/8.1 methods that maybe primarily use older software program, it’s doable this runtime has not been put in by the person (or by purposes they use). As a consequence, the uninstall payload will crash because it can’t efficiently resolve its dependencies.
  2. The command kind 42 that’s used to deploy the shellcode is a comparatively latest addition to QakBot. It first appeared in November 2022. Older variations don’t perceive this command – they return an error code (-2) to the server. In exams we ran, the server ignores this response and retains sending the identical unsupported command time and again. Admittely, it’s questionable whether or not previous infections (e.g., as a result of an contaminated system or VM has been offline for a chronic interval) may even attain the C2 infrastructure attributable to previous server lists. One other doable situation could be that the malware did not correctly replace itself to a more recent binary model for no matter cause, however continues to be in touch with the servers.

Since most individuals are on Home windows 10/11 these days, generally this could work advantageous and virtually take away the QakBot an infection from the system. And even when the bot lingers on older methods, it’s comparatively innocent as a result of it both can’t discover a working server, or the server is underneath management of regulation enforcement and thus shouldn’t ship any instructions that trigger additional hurt.

SHA256 of the total shellcode: 7cdee5a583eacf24b1f142413aabb4e556ccf4ef3a4764ad084c1526cc90e117
SHA256 of the decrypted library: fab408536aa37c4abc8be97ab9c1f86cb33b63923d423fdc2859eb9d63fa8ea0

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