Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:9 relevant versions.
The compile_branch function in PCRE before 8.37 allows context-dependent attackers to compile incorrect code, cause a denial of service (out-of-bounds heap read and crash), or possibly have other unspecified impact via a regular expression with a group containing a forward reference repeated a large number of times within a repeated outer group that has a zero minimum quantifier.
pcre3 to version 2:8.35-7.2 or higher.