CVE-2014-0050: Apache Tomcat vulnerable to Denial of service attack

If you are a developer, you should always be careful when writing loops especially an endless loops [ for(;;) or while(true) ] which are coded to be stopped by an 'if' statement. 

Security researchers from TrustWave have explained how an endless 'for' loop resulted in a denial of service vulnerability that could allow attackers to launch DOS attacks against websites hosted on Apache Tomcat servers.

The vulnerability(CVE-2014-0050) is located in Apache Commons FileUpload file.  The 'for' loop in the file is coded in such a way that it will be stopped by raising an exception or by returning a value.  

An attacker can send a malformed 'Content-type' header for a multipart request which could result in an infinite loop. 

Multipart is often used in HTTP request for uploading files.  Values in the multipart requests are separated by a magic line called "boundary".  Boundary is a random string which will be defined in the 'content-type' header.

By sending a boundary value longer than 4091 characters and 'body' longer than 4096 characters, the 'for' loop won't be stopped by both 'if' statement. 

TrustWave researchers managed to send four times a request containing more than 4091 characters in the boundary field that forces vulnerable tomcat server into an infinite loop.  As a result, the tomcat server will end up in consuming all available CPU resources until it is stopped.

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