Monday, November 21, 2011

ZeroAccess Rootkit Launched by Signed Installers

Via McAfee Labs -

Digital certificates and certificate authorities have been much in the news recently. Attacks–such as those used by Stuxnet, Duqu, and other malware–involving stolen certificates show an increasingly worrisome new security trend.

Certificate authorities have been targeted several times in the recent past with some success. There is a large chunk of known malware signed by apparently legitimate companies that appear to have authored malware, adware, and/or potentially unwanted programs. As a matter of fact, a very significant percentage of recent malware executables (as high as 5 percent) purport to be, or are, signed with some sort of certificate. Even in the case of mobile malware, signed executables have appeared because issuers have failed to see the malware in the files before approving them. This attention to certificates by malware authors seems to validate that they are indeed the “keys to the kingdom.”

A few days ago, we first saw a new attack that turned out to be variants of the infamous ZeroAccess rootkit, launched by digitally signed installers and uninstallers.


ZeroAccess is known to be very difficult to remove from system. It has a variety of techniques to fight against antivirus and security products, and can do so generically. Previously, we discussed how the rootkit can generically kill AV and security products, using user mode APC calls from kernel mode. This attack is very serious, and successful against most targets.

This version of ZeroAccess uses another neat trick to also generically target certain security products. Once ZeroAccess is loaded, it prevents the execution of several security products by mimicking a load error.


Several installers and uninstallers have been observed, with variants of ZeroAccess. Those that we are aware of can be cleaned with the free McAfee Labs tool RootkitRemover, which is available for download.


Free ZeroAccess removal tool from McAfee Labs, RootkitRemover, available at

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