CVE 2009-5155
In the GNU C Library (aka glibc or libc6) before 2.28, parse_reg_exp in posix/regcomp.c misparses alternatives, which allows attackers to cause a denial of service (assertion failure and application exit) or trigger an incorrect result by attempting a regular-expression match.
See the 
CVE page on Mitre.org
for more details.
