Rack before 1.1.3, 1.2.x before 1.2.5, and 1.3.x before 1.3.6 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.
https://github.com/advisories/GHSA-v6j3-7jrw-hq2p
https://gist.github.com/52bbc6b9cc19ce330829
https://euvd.enisa.europa.eu/vulnerability/EUVD-2022-5298
http://www.ocert.org/advisories/ocert-2011-003.html
http://www.nruns.com/_downloads/advisory28122011.pdf
http://www.kb.cert.org/vuls/id/903934
http://www.debian.org/security/2013/dsa-2783
http://archives.neohapsis.com/archives/bugtraq/2011-12/0181.html