A vulnerability has been identified in Microsoft Internet Information Services (IIS) where the server in incorrectly handling files with multiple extensions separated by the ";" character such as "malicious.asp;.jpg" as an ASP file. This could allow attackers to upload malicious executables on a vulnerable web server, bypassing file extension protections and restrictions. This vulnerability does not work with ASP.Net.

Pending an IIS security patch, some workaround are available here.
 

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Guy Bruneau IPSS Inc. gbruneau at isc dot sans dot org