This module triggers a use-after-free vulnerability in the Apache
Software Foundation mod_isapi extension for versions 2.2.14 and earlier.
In order to reach the vulnerable code, the target server must have an
ISAPI module installed and configured.
By making a request that terminates abnormally (either an aborted TCP
connection or an unsatisfied chunked request), mod_isapi will unload the
ISAPI extension. Later, if another request comes for that ISAPI module,
previously obtained pointers will be used resulting in an access
violation or potentially arbitrary code execution.
Although arbitrary code execution is theoretically possible, a
real-world method of invoking this consequence has not been proven. In
order to do so, one would need to find a situation where a particular
ISAPI module loads at an image base address that can be re-allocated by
a remote attacker.
Limited success was encountered using two separate ISAPI modules. In
this scenario, a second ISAPI module was loaded into the same memory
area as the previously unloaded module.
- Brett Gervasoni
- jduck <email@example.com>