PetitPotam Vulnerability Exploited in Ransomware Attacks

The recently disclosed Windows Server vulnerability dubbed “PetitPotam” is being actively exploited in malicious attacks, including some aimed at deploying a piece of ransomware named LockFile.

Tracked as CVE-2021-36942, PetitPotam is a vulnerability that can help an attacker take complete control of Windows domains.

Microsoft released patches for the vulnerability as part of its August 2021 set of security updates, but Slovenia-based ACROS Security says that the fixes are incomplete.

In a blog post last week, security researchers with Symantec, which is now part of Broadcom Software, revealed that PetitPotam is being exploited in attacks featuring the LockFile ransomware, but only post-exploitation, to take over domain controllers.

“Indications are that the attackers gain access to victims’ networks via Microsoft Exchange Servers, and then use the incompletely patched PetitPotam vulnerability to gain access to the domain controller, and then spread across the network. It is not clear how the attackers gain initial access to the Microsoft Exchange Servers,” Symantec’s researchers say.

Targeted organizations span across multiple sectors, including business services, financial services, engineering, legal, manufacturing, and travel and tourism.

LockFile is a rather novel ransomware family that was initially discovered within a compromised environment about a month ago. Since then, more than 10 organizations have been infected, Symantec says.

After compromising Exchange servers, likely by exploiting the ProxyShell vulnerabilities, the attackers execute PowerShell commands to download attack tools and maintain access to the victim environment. Days later, the attackers start deploying ransomware.

Shortly after the ransomware is executed, the attackers deploy on the compromised Exchange server an exploit for PetitPotam, along with files to facilitate the exploitation, Symantec says.

After successfully taking over the domain controller, the attackers copy the LockFile ransomware and additional files to a directory used to deploy scripts to network clients. Thus, the ransomware is executed on all clients that authenticate to the controller.

“LockFile appears to be a new threat on the already crowded ransomware landscape. The investigation into this threat, and whether it may have links to any previously seen or retired ransomware threats continues,” Symantec notes.

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