A flaw that was fixed in 1.4.4, 1.3.9, 1.2.7, and 1.1.5 was also announced [4] that creates a minor denial of service condition, this time in the Rack::Auth::AbstractRequest, where it symbolized arbitrary strings (apparently this has something to do with authentication, but there is no further information provided other than the fix [5] itself, which is noted as "a breaking API change").

[4] https://groups.google.com/forum/#!topic/rack-devel/ImYOqcGiksw/discussion [5] https://github.com/rack/rack/commit/0c76175fcccad74ba2f991c487d3669c28a297c8

lib/rack/multipart.rb in Rack before 1.1.4, 1.2.x before 1.2.6, 1.3.x before 1.3.7, and 1.4.x before 1.4.2 uses an incorrect regular expression, which allows remote attackers to cause a denial of service (infinite loop) via a crafted Content-Disposion header.