Home Security CCleaner malware: Avast admits it was wrong on payload

CCleaner malware: Avast admits it was wrong on payload

Czech cyber security company Avast has substantiated the findings by Cisco's Talos Intelligence Group that malware hidden in CCleaner, a popular application that allows Windows users to perform routine maintenance on their systems, was aimed at big technology companies in the US, Europe and Asia.

It has also had to backtrack on an earlier claim that a second-stage payload of the malware in question was never delivered to any targets.

"...the attack was targeting select large technology and telecommunication companies in Japan, Taiwan, UK, Germany and the US," a blog post by Avast chief executive Vince Steckler and chief technology officer Ondřej Vlček said.

The news that CCleaner, an app made by Piriform, a company which Avast acquired recently, had been compromised, broke on 17 September, through a detailed report from Talos.

The same group published a second analysis on Wednesday, detailing a number of companies that it said were targeted by the malware within CCleaner. Listed were Cisco, Intel, Microsoft, HTC, Samsung, VMware,Akamai, Sony, Singtel, D-Link, O2, Vodafone, German gaming and gambling company Gauselmann, Linksys, Gmail, MSI, Dynamic Network Services and Epson.

Avast did not name any of the companies but only confirmed that the malware was an advanced persistent threat which had been written in such a way as to deliver a second-stage payload to specific targets.

"Specifically, the server logs indicated 20 machines in a total of eight organisations to which the second stage payload was sent, but given that the logs were only collected for little over three days, the actual number of computers that received the second stage payload was likely at least in the order of hundreds," Steckler and Vlček said.

"This is a change from our previous statement, in which we said that to the best of our knowledge, the second stage payload never delivered."

In that previous statement, Avast had said: "...the offending CnC server was taken down on September 15, 9:50 AM PT, following Avast collaboration with law enforcement. During that time, the Cisco Talos team, who has been working on this issue in parallel, registered the secondary DGA domains before we had the chance to. With these two actions, the server was taken down and the threat was effectively eliminated as the attacker lost the ability to deliver the payload."

The two Avast officials said that given that CCleaner was a consumer-oriented product, "this was a typical watering hole attack where the vast majority of users were uninteresting for the attacker, but select ones were".

The Talos team had said in its second analysis that merely updating CCleaner to its latest version did not mitigate the threat.

It said that its new findings "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 back-ups 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".

But Steckler and Vlček wrote: "...we stand by the recommendation to upgrade CCleaner to the latest version (now 5.35, after we have revoked the signing certificate used to sign the impacted version 5.33) and use a quality anti-virus product...

"For corporate users, the decision may be different and will likely depend on corporate IT policies. At this stage, we cannot state that the corporate machines could not be compromised, even though the attack was highly targeted."

The two officials said more updates would be provided as the matter progressed.

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Sam Varghese

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A professional journalist with decades of experience, Sam for nine years used DOS and then Windows, which led him to start experimenting with GNU/Linux in 1998. Since then he has written widely about the use of both free and open source software, and the people behind the code. His personal blog is titled Irregular Expression.