Microsoft is releasing an out-of-band security update today for an ASP.NET Security Vulnerability revealed yesterday, December 28, 2011.

The update overcomes a security hole that could be used to launch Denial of Service attacks, though Microsoft says it is currently unaware of any attacks on ASP.NET customers using this exploit.

The problem doesn’t just affect ASP.NET; the method described would work with products including PHP 4 and 5, Java, Apache Tomcat and Geronimo, Jetty, Oracle Glassfish, Python, Plone, CRuby 1.8, JRuby and Rubinius v8, according to details posted on the gmane.comp.security full disclosure mailing list.

The details of the potential attack method were given at the Chaos Communication Congress conference, where security researchers Julian Wälde and Alexander Klink showed a new way to attack Web Application Frameworks which exploits hash-table data-structures.

According to Microsoft’s Security Bulletin, hash collision attacks attempt to populate a hash-table within a server app with large numbers of items whose keys resolve to the same hash code. These key collisions can significantly slow down operations on the hash-table, and with enough elements can cause a server to spend minutes (or even hours) processing them. This can block a web server from processing requests from other users, and cause a denial of service.

The bulletin also points out that because these attacks on web frameworks can create Denial of Service issues with relatively few HTTP requests, there is a high likelihood of attacks happening using this approach.

It’s worth noting that if your site disallows application/x-www-form-urlencoded or multipart/form-data HTTP content types, it won’t be vulnerable. However, Microsoft is releasing an out-of-band security update on Thursday, December 29 at approximately 10am Pacific Time.

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