A global buffer overflow in OptiPNG 0.7.6 allows remote attackers to cause a denial-of-service attack or other unspecified impact with a maliciously crafted GIF format file, related to an uncontrolled loop in the LZWReadByte function of the gifread.c file.
https://www.debian.org/security/2017/dsa-4058
https://sourceforge.net/p/optipng/bugs/69/
https://security.gentoo.org/glsa/201801-02
https://lists.debian.org/debian-lts-announce/2017/11/msg00042.html