Uninformed: Informative Information for the Uninformed

Vol 5» 2006.Sep

Preventing the Exploitation of SEH Overwrites
This paper proposes a technique that can be used to prevent the exploitation of SEH overwrites on 32-bit Windows applications without requiring any recompilation. While Microsoft has attempted to address this attack vector through changes to the exception dispatcher and through enhanced compiler support, such as with /SAFESEH and /GS, the majority of benefits they offer are limited to image files that have been compiled to make use of the compiler enhancements. This limitation means that without all image files being compiled with these enhancements, it may still be possible to leverage an SEH overwrite to gain code execution. In particular, many third-party applications are still vulnerable to SEH overwrites even on the latest versions of Windows because they have not been recompiled to incorporate these enhancements. To that point, the technique described in this paper does not rely on any compile time support and instead can be applied at runtime to existing applications without any noticeable performance degradation. This technique is also backward compatible with all versions of Windows NT+, thus making it a viable and proactive solution for legacy installations.
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