Security researchers have identified a two-stage back door embedded in CCleaner 5.33.6162 and CCleaner Cloud version 1.07.3191 (32-bit only for both versions). CCleaner is a legitimate Windows cleanup utility distributed by Piriform, a company owned by the antivirus vendor Avast. The back door was introduced via a supply chain compromise that allowed the attacker to insert malicious code into a legitimate installer file from the official Piriform servers. Versions prior to 5.33 are not affected, and version 5.34 has been released to remove the malicious code.
Conduct anti-virus/anti-malware scans on any machines where CCleaner is known to be installed.
Update CCleaner to version 5.34 and CCleaner Cloud to version 1.07.3214.
The following SHA-256 file hashes are linked to the Floxif Trojan that is embedded in the affected CCleaner versions:
The hardcoded C2 server is currently unreachable and the fallback DGA domains are not controlled by the attacker. No documented instances of second stage payload activation have been reported at this time.
Please see the official Piriform Security Notification for more information: