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Apache mod_isapi Dangling Pointer

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Apache mod_isapi Dangling Pointer



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 <jduck@metasploit.com>


Module Options

To display the available options, load the module within the Metasploit console and run the commands 'show options' or 'show advanced':

msf > use auxiliary/dos/http/apache_mod_isapi
msf auxiliary(apache_mod_isapi) > show actions
msf auxiliary(apache_mod_isapi) > set ACTION < action-name >
msf auxiliary(apache_mod_isapi) > show options
    ...show and set options...
msf auxiliary(apache_mod_isapi) > run 

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