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Microsoft confirms code-execution bug in Windows apps

'Cannot directly be addressed in Windows'

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Microsoft on Monday warned of a vulnerability in Windows applications made by third-party developers that allows remote attackers to execute malicious code on end-user PCs.

The company's security team is still investigating whether any Microsoft programs are susceptible to the so-called binary planting or DLL preloading attacks. Until patches are available, it said admins should run a new software tool that changes the way Windows loads application library files or disable several networking features to blunt attempts to exploit the flaw.

“Loading dynamic libraries is basic behavior for Windows and other operating systems, and the design of some applications require the ability to load libraries from the current working directory,” members of the Microsoft Security Response Center wrote here. “Hence, this issue cannot directly be addressed in Windows without breaking expected functionality. Instead, it requires developers to ensure they code secure library loads.”

The advisory confirmed previous reports that the attacks exploit a weakness in the way programs load associated libraries. The corresponding binary files can be located in a variety of directories, including those on networks controlled by a malicious hacker.

The attack works because many applications ignore best security practices and search for the library based only on the file name, rather than the full directory path, the advisory said. When the current working directory is set to one controlled by the attacker, it's possible to cause load a malicious file.

The advisory didn't say how many applications are vulnerable. In an interview last week, Mitja Kolsek, CEO of application security firm Acros Security, said his company has identified about 200 Windows susceptible programs and warned there could be more.

H D Moore, CSO and chief architect of the Metasploit project, has said at least one component of Windows is also vulnerable.

Microsoft's advisory repeated Moore's previous guidance that admins disable WebDAV and block outgoing SMB connections on ports 445 and 139. Redmond has also released a software tool that changes the way Windows searches for DLL files. Different versions of Windows requires a specific versions of the tools. Download locations are here. Microsoft has additional details here and here.

Moore has also published this post with a wealth of information. ®

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