GandCrab Ransomware Continues to Evolve But Can't Spread Via SMB Shares Yet

The authors of GandCrab, a ransomware sample that in less than six months has become the biggest threat in its category, are continuing to update and tweak the malware to make it harder to stop. But fears in recent days that they might have added a new WannaCry-like capability for spreading GandCrab via SMB shares appear unfounded at the moment.

Security vendor Fortinet recently discovered a new version (4.1) of GandCrab in the wild. Like its predecessor, released just two days prior to the new discovery, the latest version is being distributed through compromised websites designed to appear like download sites for cracked applications. And as with version 4, version 4.1, like the Petya ransomware tool, also uses the faster Salsa2.0 stream cipher to encrypt data instead of the RSA-2048 encryption used in early GandCrab releases.

The biggest difference in GandCrab 4.1 is that it contains a long, hard-coded list of websites to which the malware connects. Once connected to a URL in the list, the malware sends it data — such as the IP address, username, computer name, network domain, and, if present, a list of anti-malware tools on the system — from the infected system.

Interestingly, according to Fortinet, there is no evidence that any one of the websites in GandCrab 4.1's hard-coded list has actually been compromised. And there's little logical reason why the authors of GandCrab would want to send victim information to so many hosts at once anyway, when all they really need is to have the information sent to one system. The only explanations, according to the security firm, are that the creators of GandCrab are testing the functionality or have put it there as a diversionary tactic.

"Unfortunately, we really don't know what the motivation behind the author truly is and how it makes sense, given that one functional URL can retrieve this information as well," says Val Saengphaibul, senior threat researcher at Fortinet's FortiGuard Labs. "It perhaps might be a smoke screen to throw off analysis or perhaps something experimental that might make sense afterward."

Fortinet's analysis also showed that GandCrab 4.1 is designed to kill numerous processes, such as msftesql.exe, sqlagent.exe, oracle.exe, msaccess.exe, powerpnt.exe, and wordpad.exe, so it can ensure full encryption of any targeted files.

Killing the processes ensures that high-value files of the victim — Microsoft Office Files, Steam, etc. — are encrypted, Saengphaibul says. "Any open, in-progress file is also shut down to allow it to be overwritten to ensure that the full encryption routine takes place on those as well," he says.

One thing that Fortinet's researchers did not find, however, is any evidence that GandCrab is now able to spread via SMB shares, such as WannaCry and Petya/NotPetya. That would have made the threat posed by the malware substantially greater.

According to the vendor, its researchers have not able to find any function in GandCrab 4.1 that would support this capability. Therefore, any fears about exploit propagation via SMB have to be considered as speculative for the moment, the vendor said.

Since first surfacing in January, GandCrab has caught the attention of the security community both for how prolific it has been and for how its authors have managed to keep one step ahead of defenders. As of March, when numbers were last available, the malware had infected over 50,000 systems and netted its operators over $600,000 in ransom payments.

Security researchers have previously noted how the creators of the tool appear to have adopted an agile-like development approach to the malware, including the way it is maintained. From an initially buggy release, the malware has kept evolving, with each version featuring tweaks designed to address shortcomings in previous iterations. Among the several updates is one that surfaced in version 4.0 that gives GandCrab the ability to encrypt data without first connecting to its C2 server, meaning it can encrypt even when an infected system is not connected to the Internet.

Even though many of the updates to the malware have been incremental in nature, they are still enough to warrant continual analysis from the security community, Saengphaibul says. "The GandCrab operation is run in true business-like fashion and focuses on a high return of infection on victims while at the same time focusing on evading antivirus technologies," he notes.

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