Apache Tomcat before 5.5.35, 6.x before 6.0.35, and 7.x before 7.0.23 computes hash values for form parameters without restricting the ability to trigger hash collisions predictably, which allows remote attackers to cause a denial of service (CPU consumption) by sending many crafted parameters.
http://marc.info/?l=bugtraq&m=132871655717248&w=2
http://marc.info/?l=bugtraq&m=133294394108746&w=2
http://marc.info/?l=bugtraq&m=136485229118404&w=2
http://rhn.redhat.com/errata/RHSA-2012-0074.html
http://rhn.redhat.com/errata/RHSA-2012-0075.html
http://rhn.redhat.com/errata/RHSA-2012-0076.html
http://rhn.redhat.com/errata/RHSA-2012-0077.html
http://rhn.redhat.com/errata/RHSA-2012-0078.html
http://rhn.redhat.com/errata/RHSA-2012-0089.html
http://rhn.redhat.com/errata/RHSA-2012-0325.html
http://rhn.redhat.com/errata/RHSA-2012-0406.html
https://bugzilla.redhat.com/show_bug.cgi?id=750521
http://secunia.com/advisories/48549
http://secunia.com/advisories/48790
http://secunia.com/advisories/48791
http://secunia.com/advisories/54971
http://secunia.com/advisories/55115
https://github.com/FireFart/HashCollision-DOS-POC/blob/master/HashtablePOC.py
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A18886
http://tomcat.apache.org/tomcat-7.0-doc/changelog.html