IIS 8 (w3wp.exe) periodically crashes due to a memory access violation in ISAPI module (disp_iis.dll).

Environment

Dispatcher 4.2.3 and prior on IIS

Cause

This issue happens when a request:

1. is declined by the dispatcher (because e.g. of its /filter settings)
2. internally redirected to an error page
3. that error page is again declined by the dispatcher

On too many subsequent errors, the Application Pool may stop, depending on its RapidFailurePolicy.

Resolution

Upgrade the dispatcher to version 4.2.4. 

** At the time of writing this article, only Dispatcher 4.2.3 is not publicly available yet.  For a pre-release build of Dispatcher 4.2.4, contact the AEM support team.