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.
https://support.f5.com/csp/article/K64119434?utm_source=f5support&%3Butm_medium=RSS
https://support.f5.com/csp/article/K64119434
https://sourceware.org/git/gitweb.cgi?p=glibc.git%3Bh=eb04c21373e2a2885f3d52ff192b0499afe3c672
https://security.netapp.com/advisory/ntap-20190315-0002/
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22793
http://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=5513b40999149090987a0341c018d05d3eea1272