Someone asked me about the Hash DoS attack recently disclosed at CCC, so I thought I would give a high level explanation of it here in case it benefits others as well. Hash tables are often used in programming languages to map data keys and values together. A comparable real world example could be a phone book which maps a person's name (the key) to their phone number (the value).
On a recent engagement we gained unrestricted administrative access to a certain proprietary web application by exploiting a Session Fixation flaw. According to the WASC Threat Classification v2, Session Fixation is an attack technique that forces a user's session ID to an explicit value.
Often when implementing customised ModSecurity solutions we need to extend the built-in functionality via Lua scripting. One of the disadvantages to this approach is the added latency penalty paid for not using the native rules language. When web site performance is critical for business continuity, every additional millesecond counts. The current trunk code fixes a long-standing limitation where ModSecurity needed to create a new VM for each request, which added latency every time a Lua script was executed.
One of the more useful features of ModSecurity is it's persistant storage capabilities. ModSecurity uses the SDBM library, which comes with the Apache Portable Runtime (APR). When using ModSecurity collections for anything beyond trivial use, you may quickly hit the arbitrary SDBM library limit of 1008 bytes. That limit is on the combined size of both the key and record length. When you hit the SDMB size limit, you get the following cryptic error message:
Recently a floating point DoS vulnerability surfaced in both PHP and Java. The crux of the problem is that PHP and Java apps go into an infinite loop and hang when trying to process numeric values in the (approximate) range of 2.2250738585072011E-208 to 2.2250738585072013E-208. For more information see here,here and here.
