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Windows 0day allows malicious code execution

Potential 'nightmare'

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Antimalware provider Prevx has sounded the alarm about a serious vulnerability in fully patched versions of Microsoft Windows. It allows attackers to execute malware, even in versions designed to withstand such exploits.

Technical details have already been published on a Chinese forum, leading to speculation that it won't be long before attackers exploit it in the wild.

“This could potentially become a nightmare due to the nature of the flaw,” Prevx researcher Marco Giuliani wrote here. “We expect to see this exploit being actively used by malwares very soon – it's an opportunity that malware writers surely won't miss.”

The flaw resides in the win32k.sys part of the Windows kernel and results from an API known as NtGdiEnableEUDC that fails to properly vet user input for harmful content. Attackers can exploit the bug to redirect overwritten return memory addresses to malicious code, which is then executed with kernel mode privileges. As a result, the flaw allows even users or processes with limited privileges to execute code will elevated rights.

“Being a privilege escalation exploit, it bypasses by design even the protection given by the User Account Control technology implemented in Windows Vista and Windows 7,” Giuliani said. “All Windows XP/Vista/7 both 32 and 64 bit are vulnerable to this attack.”

Microsoft "is aware of the issue and it is under investigation," according to a statement, which a spokeswoman attributed to Jerry Bryant, Group Manager of the company's Response Communications.

On Wednesday evening, Microsoft Security Response tweeted: "We're investigating public PoC for a local EoP vuln requiring an account on the target system."

No further details were available at time of writing. If confirmed, the unpatched vulnerability would be the second known 0day to affect a widely used piece of Microsoft software. Earler this month, researchers unearthed an unrelated security bug in earlier versions of Internet Explorer that is being exploited on compromised websites. ® ®

This article was updated to include MSR's tweet.

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