Microsoft confirms 0-Day IIS security vulnerability

Microsoft has confirmed officially a zero-day security vulnerability affecting Internet Information Services (IIS). The security hole was initially reported just ahead of Christmas on December 23rd, and the Redmond company provided the first response at the end of the past week. So far, the issue in question affects version 6 of IIS on a fully patched Windows Server 2003 R2 SP2; however, additional IIS
releases might also be impacted. A Microsoft security program manager notes that

Microsoft is aware of the problem and that investigation into the matter has already been kicked off. At the same time, the program manager assured customers running IIS that it hasn’t detected any active attacks in the wild targeting the new 0-day flaw.

The vulnerability identified in Microsoft Internet Information Services (IIS) involves the incorrect manner in which the server deals with files with multiple extensions. As long as the multiple extensions are divided by the “;” character, the IIS server handles them as ASP files.

A possible attacks scenario could be based on an exploit constructed out of malformed executables. Any malicious files uploaded to a vulnerable web server would circumvent any file extension protections and restrictions in place.

More/.........Microsoft Confirms 0-Day IIS Security Vulnerability - IIS 6.0 Security Best Practices can help mitigate the threat - Softpedia

Update:

We’ve completed our investigation into the claims that came up over the holiday of a possible vulnerability in IIS and found that there is no vulnerability in IIS.

What we have seen is that there is an inconsistency in IIS 6 only in how it handles semicolons in URLs. It’s this inconsistency that the claims have focused on, saying this enables an attacker to bypass content filtering software to upload and execute code on an IIS server.

The key in this is the last point: for the scenario to work, the IIS server must already be configured to allow both “write” and “execute” privileges on the same directory. This is not the default configuration for IIS and is contrary to all of our published best practices. Quite simply, an IIS server configured in this manner is inherently vulnerable to attack.

See the complete report at The Microsoft Security Response Center (MSRC) : Results of Investigation into Holiday IIS Claim