Microsoft Confirms Windows DLL Hijacking Vulnerabilities

Numerous applications for the Microsoft Windows operating system are vulnerable to a remote execution attack, Microsoft confirmed Monday.

The vulnerability stems from the manner in which some Windows applications process DLL files. "DLL hijacking attacks are targeted at Windows applications -- third party and Microsoft -- that have not followed recommended security practices and can be tricked to load DLLs from locations that are owned by the attacker," said Wolfgang Kandek, chief technology officer at Qualys, in a blog post. But if attackers disguise malicious code as a DLL file, which an application then executes, then the code can provide the attacker with control of the machine.

For this bug at least, blame application programmers. "This issue is caused by specific insecure programming practices that allow so-called 'binary planting' or 'DLL preloading attacks,'" Microsoft confirmed yesterday in a security advisory.

The company reiterated its existing advice for using safe techniques for loading external libraries. It also noted that for a DLL hijacking attack to be successful, a user would have to visit a remote file system or WebDAV share, then open a document from this location. To that end, Microsoft also released a hotfix for controlling the DLL search path algorithm.

To mitigate the vulnerability, "we recommend installing the hotfix," said Kundek, as well as "setting the registry to not allow loading of binaries via network shares and WebDAV (setting 2) as soon as possible."

Microsoft is still investigating its own products to see which are affected by the DLL vulnerability. The DLL vulnerability was first documented earlier this year in a paper titled Automatic Detection of Vulnerable Dynamic Component Loading by researchers Taeho Kwon and Zhendong Su from the University of California at Davis.

But the vulnerability gained attention last week due to a security advisory from Slovenian security firm Acros, which labeled it as a binary planting flaw in iTunes.

Many more applications appear to be infected. "While working on the Windows Shortcut exploit, I stumbled on this class of bugs and identified a couple dozen applications that seemed to be affected by this problem," said HD Moore, chief security officer at Rapid7 and chief architect of the Metasploit Framework, an open source penetration testing platform, on the Rapid7 blog.

He's added a DLL exploit capability to Metasploit, meaning that anyone can now study the attack and see how it works, as well as unearth more vulnerable applications.