Does anybody know anything more concrete? Knowing that there are "some"
vulnerabilities with "unknown impact" isn't particularly helpful. Flex doesn't
manage a changelog. In NEWS, the most concrete is "numerous bug and security
fixes"...

This issue does not affect the version of flex we ship in Fedora Core 4 or 5,
nor do any of the prebuilt flex files contained in any source files suffer from
this exploit.  The Red Hat Security Response Team did a very through analysis of
this problem in order to come to this conclusion.

The problem is that in newer versions of flex don't allocate enough space for
the pattern state machine.  The old versions of flex used static arrays, where
the newer versions dynamically allocate the space needed.  This dynamic
allocation incorrectly calculated the space required.

The flex commit is here:
http://cvs.sourceforge.net/viewcvs.py/flex/flex/flex.skl?rev=2.193&view=auto