SonicWall Devices Infected by Persistent Malware
SonicWall devices are being attacked by some very persistent malware that is capable of surviving through multiple firmware updates, experts have claimed. Cybersecurity researchers from Mandiant and SonicWall recently discovered a custom-built malware, designed specifically for SonicWall Secure Mobile Access (SMA) appliances, most likely designed by a Chinese threat actor dubbed UNC4540.
Understanding the Malware
The malware shows a deep understanding of the devices it was built for and is designed for espionage. It is capable of stealing user passwords and providing shell access. The overall behavior of the suite of malicious bash scripts shows a detailed understanding of the appliance and is well-tailored to the system to provide stability and persistence, Mandiant said.
Establishing Remote Access
The main module can steal hashed credentials of all users that are logged into the compromised endpoints, copy them into a text file, and ship them out to be decrypted elsewhere. Another module establishes a reverse shell for easy remote access. The researchers also found a module that adds a small patch to a legitimate SonicWall binary whose purpose they still weren’t able to determine.
The researchers couldn’t determine which vulnerability the attackers used to compromise these devices with malware, but they suspect the malware was deployed years ago and successfully lived through multiple firmware updates. They believe the initial compromise could have been done back in 2021.
Protecting Your Devices
To protect your devices against unknown threats such as this one, the best course of action is to apply the latest security updates. SonicWall’s latest version for targeted appliances is 10.2.1.7, which includes File Integrity Monitoring (FIM) and anomalous process identification, two features which should detect and stop this threat.
In recent years, Chinese attackers have deployed multiple zero-day exploits and malware for a variety of internet-facing network appliances as a route to full enterprise intrusion, and the instance reported here is part of a recent pattern that Mandiant expects to continue in the near term, Mandiant concluded.
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