CCleaner Malware uses Secondary Backdoor to Infect Tech Companies

A group of unknown hackers, which hijacked CCleaner’s download server to distribute a malicious version of the system optimization software, targeted at least 20 major international technology companies with a secondary payload.

Beginning of this week, when the hack was reported, researchers assured users that there’s no second stage malware used in the massive attack and affected users can simply update their version in order to get rid of the malicious software.

During an examination of the hackers’ “C2” server, to which the malicious CCleaner versions connected, security researchers from Cisco’s Talos Group found evidence of a secondary payload (named GeeSetup_x86.dll, a backdoor module), that was delivered to a specific list of computers based on local domain names.

A predefined list, mentioned in the configuration of the C2 server, is revealing, that the attack is intended to find computers inside the networks of the major technology firms and deliver the secondary payload.

The target companies included:

Google, Microsoft, Cisco, Intel, Samsung, Sony, HTC, Linksys, D-Link, Akamai, VMware

In the initial database, researchers found a list of nearly 700,000 machines infected with the malicious version of CCleaner, and a list of at least 20 machines that were infected with the secondary payload to get a deeper foothold on those systems.

“The CCleaner hackers specifically chose these 20 machines based upon their Domain name, IP address, and Hostname. The researchers believe the secondary malware was likely intended for industrial espionage.” Says Mohit Kumar.

According to the researchers from Kaspersky, the CCleaner malware shares some code with the hacking tools used by a sophisticated Chinese hacking group called Axiom, also known as APT17, Group 72, DeputyDog, Tailgater Team, Hidden Lynx or AuroraPanda.

“The malware injected into #CCleaner has shared code with several tools used by one of the APT groups from the #Axiom APT ‘umbrella’,” tweeted director of Global Research and Analysis Team at Kaspersky Lab.

Also, Cisco researchers said, that they have notified the affected tech companies about the breach.

Simply removing the Avast’s software application from the infected machines would not be enough, to get rid of the CCleaner second stage malware payload from their network, with the attackers’ server being still active.

Companies that have had their computers infected with the malicious version of CCleaner, are strongly encouraged to completely restore their systems, from backup versions, before the installation of the tainted security program.

“These findings also support and reinforce our previous recommendation that those impacted by this supply chain attack should not simply remove the affected version of CCleaner or update to the latest version, but should restore from backups or reimage systems to ensure that they completely remove not only the backdoored version of CCleaner but also any other malware that may be resident on the system,” the researchers say.

The Windows 32-bit version of CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 were affected by the malware, users should update to version 5.34 and up.