Microsoft released an advance notification for an out-of-band security update to address the publicly disclosed "denial-of-service" vulnerability affecting several vendors' web application platforms, including Microsoft's ASP.NET, as described in Security Advisory 2659883.
"This vulnerability could allow an anonymous attacker to efficiently consume all CPU resources on a web server, or even on a cluster of web servers. For ASP.NET in particular, a single specially crafted ~100kb HTTP request can consume 100% of one CPU core for between 90 - 110 seconds. An attacker could potentially repeatedly issue such requests, causing performance to degrade significantly enough to cause a denial of service condition for even multi-core servers or clusters of servers," revealed Microsoft's Security Research & Defense.
Adding, the SRD team says "We anticipate the imminent public release of exploit code. Therefore, we encourage ASP.NET website owners to review the Security Advisory 2659883 and this blog post to evaluate the denial-of-service risk to your web property and to implement the workaround and/or attack detection mechanisms until a security update is available to comprehensively address the issue."
"The root cause of the vulnerability is a computationally expensive hash table insertion mechanism triggered by an HTTP request containing thousands and thousands of form values. Therefore, any ASP.NET website that accepts requests having HTTP content types application/x-www-form-urlencoded or multipart/form-data are likely to be vulnerable. This includes the default configuration of IIS when ASP.NET is enabled and also the majority of real-world ASP.NET websites," explains SR&D.
The release is scheduled for tomorrow, December 29, at approximately 10 a.m. PST.