Backdoor Trojan Found in 32-bit CCleaner Version 5.33.6162 and CCleaner Cloud Version 1.07.3191

The Threat

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.

Recommended Action

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.

Additional Information

The following SHA-256 file hashes are linked to the Floxif Trojan that is embedded in the affected CCleaner versions:

6f7840c77f99049d788155c1351e1560b62b8ad18ad0e9adda8218b9f432f0a9
1a4a5123d7b2c534cb3e3168f7032cf9ebf38b9a2a97226d0fdb7933cf6030ff
36b36ee9515e0a60629d2c722b006b33e543dce1c8c2611053e0651a0bfdb2e9

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:

https://www.piriform.com/news/blog/2017/9/18/security-notification-for-ccleaner-v5336162-and-ccleaner-cloud-v1073191-for-32-bit-windows-users