File Extension Bypass Vulnerability in Microsoft Internet Information Services

CVE-2009-4444

Summary

The vulnerability in Microsoft Internet Information Services (IIS) 5.x and 6.x arises from the improper handling of filename extensions. Specifically, the server evaluates only the portion of the filename preceding a semicolon, which can be exploited by attackers to circumvent file extension restrictions imposed by third-party upload applications. This flaw allows the use of dangerous extensions like .asp, .cer, and .asa with a semicolon followed by a benign extension (e.g., .jpg), potentially leading to unauthorized access to sensitive functionalities enabled by these script types.

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