Firefox onUnload + document.write() memory corruption vulnerability (MSIE7 null ptr)

[Michal Zalewski <lcamtuf () dione ids pl>]

While researching my previous report on MSIE7 browser entrapment, I
noticed that Firefox is susceptible to a pretty nasty, and apparently
easily exploitable memory corruption vulnerability. When a location
transition occurs and the structure of a document is modified from within
onUnload event handler, freed memory structures are left in inconsistent
state, possibly leading to a remote compromise.

A quick test case that crashes while trying to follow partly
user-dependent corrupted pointers near valid memory regions (can be forced
to write, too):

  http://lcamtuf.coredump.cx/ietrap/testme.html

This also crashes MSIE7 with a seemingly harmless NULL pointer bug (didn't
research it - do your homework).

Firefox problem is being tracked here:
  https://bugzilla.mozilla.org/show_bug.cgi?id=371321

/mz