Security Researcher Reveals New Windows Zero-Day Flaw

Dennis Faas's picture

A new zero-day security flaw has been found in Windows that could allow a hacker remote access to a PC. A security researcher recently disclosed the bug, which Microsoft is currently investigating.

The programming code for the security flaw has been posted publically and is related to a Windows system file called "mrxsmb.sys". The file is related to Windows Server Message Block (SMB) protocol, used for network communications.

Bug Rated Critical by Security Experts

In short, the affected file is associated with file and printer sharing features within the Windows operating system (OS).

Because this is such a sensitive part of the operating system, experts, including French security firm Vupen, have already dubbed the bug "critical," typically the highest alert level for a flaw of this kind. Vupen says a hacker with knowledge of the exploit could "cause a denial of service or take complete control of a vulnerable system." (Source:

Secunia, a Danish security firm, agreed that the bug could be used to hijack a PC. "Successful exploitation may allow execution of arbitrary code," Secunia representatives recently stated.

Unclear Which Versions of Windows are Vulnerable

It's not yet been confirmed exactly which versions of Windows are affected. Thus far it seems Windows XP and Windows Server 2003 SP2 are most definitely vulnerable, though Secunia suspects Windows Vista and Windows 7 could also be open to attack.

There's still a lot of time until Microsoft's next scheduled Patch Tuesday (March 8), meaning the company will have to determine if the bug warrants and out-of-schedule emergency fix.

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