An issue was discovered in ytnef before 1.9.1. This is related to a patch described as "2 of 9. Infinite Loop / DoS in the TNEFFillMapi function in lib/ytnef.c."
https://www.x41-dsec.de/lab/advisories/x41-2017-002-ytnef/
https://github.com/Yeraze/ytnef/pull/27
http://www.securityfocus.com/bid/96423