The TNEFFillMapi function in lib/ytnef.c in libytnef in ytnef through 1.9.2 does not ensure a nonzero count value before a certain memory allocation, which allows remote attackers to cause a denial of service (heap-based buffer overflow and application crash) or possibly have unspecified other impact via a crafted tnef file.
https://usn.ubuntu.com/3667-1/