CVE-2013-0263 rubygem-rack: Timing attack in cookie sessions

Rack::Session::Cookie in Rack 1.5.x before 1.5.2, 1.4.x before 1.4.5,
1.3.x before 1.3.10, 1.2.x before 1.2.8, and 1.1.x before 1.1.6 allows remote attackers
to guess the session cookie, gain privileges, and execute arbitrary code via a timing
attack involving an HMAC comparison function that does not run in constant time.