In ImageMagick 7.0.7-16 Q16 x86_64 2017-12-21, there is a heap-based buffer over-read in ReadOneMNGImage in coders/png.c, related to length calculation and caused by an off-by-one error.
https://www.debian.org/security/2018/dsa-4204
https://www.debian.org/security/2017/dsa-4074
https://usn.ubuntu.com/3681-1/
https://lists.debian.org/debian-lts-announce/2018/01/msg00000.html