Toby Beaumont has reported a vulnerability in Microsoft .NET Framework, which can be exploited by malicious people to bypass certain security restrictions.

The vulnerability is caused due to a canonicalization error in the ASP.NET component's authentication schema when validating URL paths. This can be exploited to bypass forms based authentication or Windows authorization configurations by using a specially crafted URL.

Example:
http://[victim]/secure%5Cfile.apx

Successful exploitation can e.g. lead to exposure of sensitive information.

Solution
Apply patches.
Further details available in Customer Area

Provided and/or discovered by
Toby Beaumont

Changelog
Further details available in Customer Area

Original Advisory
MS05-004 (KB887219):
http://www.microsoft.com/technet/security/bulletin/ms05-004.mspx

Other references
Further details available in Customer Area

Deep Links
Links available in Customer Area