FIN8 Group Uses Sardonic Backdoor for BlackCat Ransomware Attacks

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The FIN8 group, aka Syssphinx, a financially motivated (FIN uses for it) cyber threat actor, has been observed using a modified version of the Sardonic backdoor to carry out BlackCat ransomware attacks.

FIN8, previously known for targeting malware-infecting point-of-sale (PoS) systems like PUNCHTRACK and BADHATCH since at least 2016, resurfaced in March 2021 with an updated version of BADHATCH, and a new customized version called Sardonic, later announced by Bitdefender, introduced the implant in August 2021.

The Sardonic backdoor is written in C++ and is capable of collecting system information, executing commands, and loading additional malware payloads as DLLs through a plugin system. However, the latest version of the backdoor contains significant changes; Most of the source code is intentionally rewritten in C to avoid detection.

In the analyzed event, Sardonic is embedded in a PowerShell script and deployed to the target system after initial access. The script then launches a .NET installer that decrypts and executes an injector module to run the implant within the newly created WmiPrvSE.exe process. Sardonic supports up to 10 interactive sessions for the threat actor to execute malicious commands and can execute additional DLLs and shellcodes through three different plug-in formats.

Among its features, the backdoor can drop arbitrary files and leak file contents from the compromised machine to the attacker’s infrastructure.

This is not the first instance of FIN8 using Sardonic in a ransomware attack; They were detected in January 2022 using the White Rabbit ransomware based on Sardonic.

The threat actor group is known to continuously improve its capabilities and malware distribution infrastructure, regularly improving its tools and tactics to avoid detection. In order not to be the target of attacks that can be carried out using Sardonic malware;

  • Using comprehensive and reliable security solutions,
  • Using current and licensed technologies,
  • Keeping the system and applications in the current version,
  • It is recommended that the shared IoC findings related to the malware campaign be blocked by the security solutions used.

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Indicator Of Compromises

 

Sha256 Hashes

05236172591d843b15987de2243ff1bfb41c7b959d7c917949a7533ed60aafd9
0980aa80e52cc18e7b3909a0173a9efb60f9d406993d26fe3af35870ef1604d0
0e11a050369010683a7ed6a51f5ec320cd885128804713bb9df0e056e29dc3b0
2d39a58887026b99176eb16c1bba4f6971c985ac9acbd9e2747dd0620548aaf3
4e73e9a546e334f0aee8da7d191c56d25e6360ba7a79dc02fe93efbd41ff7aa4
5b8b732d0bb708aa51ac7f8a4ff5ca5ea99a84112b8b22d13674da7a8ca18c28
64f8ac7b3b28d763f0a8f6cdb4ce1e5e3892b0338c9240f27057dd9e087e3111
6cba6d8a1a73572a1a49372c9b7adfa471a3a1302dc71c4547685bcbb1eda432
72fd2f51f36ba6c842fdc801464a49dce28bd851589c7401f64bbc4f1a468b1a
827448cf3c7ddc67dca6618f4c8b1197ee2abe3526e27052d09948da2bc500ea
8cfb05cde6af3cf4e0cb025faa597c2641a4ab372268823a29baef37c6c45946
ede6ca7c3c3aedeb70e8504e1df70988263aab60ac664d03995bce645dff0935
edfd3ae4def3ddffb37bad3424eb73c17e156ba5f63fd1d651df2f5b8e34a6c7

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You can find these IoCs, and IoCs belong to other ransomware groups on our GitHub Repo.

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