The 5.2.6 release of MovableType fixed a vulnerability in the handling
of comments to blog posts. The 'comment_state' parameter is processed by
MovableType's unserialize() function which can be used to send data into
Storable::thaw().
As documented by the perl-security team recently, Storable::thaw is
unsafe to use on untrusted inputs.
http://perl5.git.perl.org/perl.git/commit/664f237a84176c09b20b62dbfe64dd736a7ce05e
The MovableType 5.2.6 release notes document the fix for this
vulnerability as:
"109458 Currently un-used parameters are unintentionally deleted when a
comment is posted"
http://www.movabletype.org/documentation/appendices/release-notes/movable-type-526-release-notes.html