The overflow protection in Expat is removed by compilers with certain optimization settings, which allows remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via crafted XML data. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-1283 and CVE-2015-2716.
https://www.tenable.com/security/tns-2016-20
https://sourceforge.net/p/expat/code_git/ci/f0bec73b018caa07d3e75ec8dd967f3785d71bde
https://security.gentoo.org/glsa/201701-21
https://kc.mcafee.com/corporate/index?page=content&id=SB10365
https://bugzilla.redhat.com/show_bug.cgi?id=1344251