AMD patches ATI Vista driver flaw

AMD has released a patch for its ATI video drivers that could allow hackers to load malware directly into Windows Vista kernel.

The flaw was discovered by security expert Joanna Rutkowska and demonstrated at the Black Hat conference last week. Another security researcher Alex Ionescu later released a proof-of-concept tool called Purple Pill that created a way of loading and unloading unsigned drivers into Vista, circumventing anti-rootkit protection that is part of Microsoft's new operating system. Ionescu promptly pulled the tool when he discovered that the flaw was not yet patched.

The flaw lies in an ATI driver called atismxx.sys, version 3.0.502.0. The vulnerability allows certain signed driver verifications for proper ATI software operations to be turned off. The exploit in the video driver could allow hackers to gain kernel access to the operating system.

According to media reports, an AMD spokesman confirmed the bug resided in a file in the installer package and would be releasing an updated version of the ATI Catalyst package today that resolved the vulnerability. He strongly urged users to download the patch to Catalyst version 7.8 from this website.

Ollie Whitehouse, a security researcher at anti-virus firm Symantec said that the tool had embedded in it a ATI signed driver that would be dropped to disk and loaded into the kernel.

"It would appear that this signed driver contained a design error which allows you to use it to load any arbitrary driver even if they are not signed," said Whitehouse. "You can imagine this came about due to a requirement to extend this core driver with arbitrary modules in ATI's design. However this has now come back and bitten them, and more so Microsoft, quite badly."

Whitehouse said that ATI would probably have to get a new certificate, sign fixed versions of all their affected drivers, and release them via Windows Update. "Only then can Microsoft get VeriSign to revoke the signing certificate. My stopwatch has started," he added.

Symantec has released a definition update covering the flaw.

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