In the GNU C Library (aka glibc or libc6) through 2.29, check_dst_limits_calc_pos_1 in posix/regexec.c has Uncontrolled Recursion, as demonstrated by '(\227|)(\\1\\1|t1|\\\2537)+' in grep.
Created glibc tracking bugs for this issue:
Affects: fedora-all [bug 1683153]
The regular expression compiler in glibc is only supposed to be exposed to trusted content, so this is not a security vulnerability:
“resource exhaustion issues which can be triggered only with crafted patterns (either during compilation or execution) are not treated as security bugs”
The regular expression compiler in glibc is only supposed to be exposed to trusted content, therefore this flaw is not classified as a security vulnerability.