Microsoft Issuing Unusual Out-of-Band Security Update

wiredmikey writes "In a rare move, Microsoft is breaking its normal procedures and will issue an emergency out-of-band security update on Thursday to address a hash collision attack vulnerability that came into the spotlight yesterday, and affects various Web platforms industry-wide. The vulnerability is not specific to Microsoft technologies and has been discovered to impact PHP 5, Java, .NET, and Google's v8, while PHP 4, Ruby, and Python are somewhat vulnerable. Microsoft plans to release the bulletin on December 29, 2011, at 10:00 AM Pacific Time, and said it would addresses security vulnerabilities in all supported releases of Microsoft Windows. 'The impact of this vulnerability is similar to other Denial of Service attacks that have been released in the past, such as the Slowloris DoS or the HTTP POST DoS,' said security expert Chris Eng. 'Unlike traditional DoS attacks, they could be conducted with very small amounts of bandwidth. This hash table multi-collision bug shares that property.'"

Comments

Re:Priorities

[nman64]

That the DDoS exists is yesterday's news (nevermind that it didn't make the Slashdot front page.) The point of this post is that Microsoft is issuing an out-of-band update. A security-aware and in-touch admin should have already learned of the n.runs advisory yesterday. If they were really on top of things, they may have been aware of the potential danger as far back as 2003.

28th chaos communication congress revelead this

[Anonymous Coward]

the Chaos Computer Club is doing their congress at the moment and the hash collision problem was topic yesterday:

28c3: Effective Denial of Service attacks against web application platforms
http://www.youtube.com/watch?v=R2Cq3CLI6H8

If using PHP5, change max_input_time

[Maow]

I agree with others, this is not a Microsoft issue, it's an issue for all sysadmins.

Anyway, from http://packetstormsecurity.org/files/108209/n.runs-SA-2011.004.txt is this helpful bit to reduce your susceptibility to attack, if you're using PHP:

The maximal POST request size is typically limited to 8 MB, which when
filled with a set of multi-collisions would consume about four hours of
CPU time on an i7 core. Luckily, this time can not be exhausted because
it is limited by the max_input_time (default configuration: -1,
unlimited), Ubuntu and several BSDs: 60 seconds) configuration
parameter. If the max_input_time parameter is set to -1 (theoretically:
unlimited), it is bound by the max_execution_time configuration
parameter (default value: 30).

Better Writeup

[inglorion_on_the_net]

Here is a better writeup from Ars Technica: http://arstechnica.com/business/news/2011/12/huge-portions-of-web-vulnerable-to-hashing-denial-of-service-attack.ars

From that page:

the flaw affects a long list of technologies, including PHP, ASP.NET, Java, Python, Ruby, Apache Tomcat, Apache Geronimo, Jetty, and Glassfish, as well as Google's open source JavaScript engine V8

the theory behind such attacks has been known since at least 2003

Klink and WÃlde showed that "PHP 5, Java, ASP.NET as well as V8 are fully vulnerable to this issue and PHP 4, Python and Ruby are partially vulnerable, depending on version or whether the server running the code is a 32-bit or 64-bit machine

The actual vulnerability seems to be that many web applications (or application servers or libraries or what have you) parse form data from HTTP POST requests into hash tables, using known hashing algorithms. If an attacker sends a POST request using specifically crafted parameter names that all hash to the same value, inserting these into the hash table will take O(n^2) time, which opens up affected software to a denial of service attack.