The _pcre32_xclass function in pcre_xclass.c in libpcre1 in PCRE 8.40 allows remote attackers to cause a denial of service (invalid memory read) via a crafted file.
https://security.gentoo.org/glsa/201710-25
https://blogs.gentoo.org/ago/2017/03/20/libpcre-invalid-memory-read-in-_pcre32_xclass-pcre_xclass-c/