Specific combination of regexp and string causes 100% CPU and doesn't recover
Specific combination of regexp and string can cause ruby process to hang with 100% CPU.
Reproducing (in irb):
/\A(?:%\h\h|[^%]+)\z/ =~ "199542328.1312293792.1.1.utmcsr%3Dgoogle%7Cutmccn%"
(above hangs indefinably with 100% cpu)
/\A(?:%\h\h|[^%]+)\z/ =~ "199542328.1312293792.1.1.utmcsr%3Dgoogle%7Cutmccn"
(same but without % at the end returns succesfully)
The code in question is found in Rack:Utils (v1.3.2, not used in v1.2.1) and can basically "kill" any server process (happened to us in production on a thin machine after we upgraded to newer rack). The above bug means that it is very easy to perform DoS on affected ruby server.