28C3 Scariest Talk of the Day

Wednesday, December 28, 2011 

We attended Effective Denial of Service attacks against web application platforms by Alexander “alech” Klink and Julian | zeri where they described a really, really easy to implement denial of service attack that exploits an artifact of hash checking which is computationally intensive when the hash table is filled with hash collisions. It is fairly easy to find 2-4 character hash collisions for a given hash functions (and there are only a few variations in use) and as hash operations are performed by default on all POST and POST-like functions, which take (by default) from 2-8MB of data, one can easily tie up a computers CPU effectively indefinitely.

The researchers tested the attack on most web languages in use (and all in common use – only Perl is deployed safe (since 2003) and Ruby 1.9 has a patch available. Every other OS is vulnerable. Today. The attack is only a POST option with a table of delimited hash collision values. You could copypasta a working exploit, it is that easy. The vast (vaaast) majority of sites on the web run PHP, and 1 Gbps of attack vector bandwidth could take down 10,000 cores. With ASP.NET, that 1 Gbps can hold down 30,000 cores cRuby 1.8 (not patched, about half of Ruby installs): that 1 Gbps can keep a million cores tied up.

Yow.

Posted at 18:32:59 UTC

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