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. (CVE-2009-5155)
Impact
An attacker can exploit this vulnerability to cause a denial-of-service (DoS) on the affected system.