The regcomp implementation in the GNU C Library (aka glibc or libc6) through 2.11.3, and 2.12.x through 2.12.2, allows context-dependent attackers to cause a denial of service (application crash) via a regular expression containing adjacent bounded repetitions that bypass the intended RE_DUP_MAX limitation, as demonstrated by a {10,}{10,}{10,}{10,}{10,} sequence in the proftpd.gnu.c exploit for ProFTPD, related to a "RE_DUP_MAX overflow."
http://www.securityfocus.com/archive/1/515589/100/0/threaded
http://www.kb.cert.org/vuls/id/912279
http://www.exploit-db.com/exploits/15935
http://securitytracker.com/id?1024832