If a Flash 9 SWF loads two SWF files with different SWF version
numbers from two distinct HTTP requests to the exact same URL
(including query string arguments), then Adobe's Flash Player plug-in
will try to dereference a null pointer.  This issue affects at least
versions 9.0.45.0, 9.0.112.0, 9.0.124.0, and 10.0.12.10 on Windows, OS
X, and Linux.  For browsers where plug-ins run in the same process
(e.g., Internet Explorer 6 and 7, Firefox 3, and Safari 3 on Windows
and OS X), this causes the entire browser process to crash.

Sample code demonstrating this issue is available at
http://www.mochimedia.com/~matthew/flashcrash/. 

On 2008.09.22, I submitted this issue to Adobe's JIRA bug tracking
system, which recorded it as issue #FP-677.  On 2008.09.23, the ticket
was changed to private for security reasons, and Adobe told me they
were able to reproduce the issue and were investigating it.  On
2008.09.26, I told Adobe I planned on submitting this issue to BugTraq
and asked if they had found any workarounds for users that I could
include.  On 2008.10.01, they told me they had resolved the problem
and that a fix will be included in the next public update, but they
did not provide any workarounds.

-- 
Matthew Dempsky
http://www.mochimedia.com