libpng vulnerabilities

Mikulas Patocka discovered that libpng incorrectly handled certain large
fields. If a user or automated system using libpng were tricked into
opening a specially crafted image, an attacker could exploit this to cause
libpng to crash, leading to a denial of service. This issue only affected
Ubuntu 12.04 LTS. (CVE-2012-3425)

Qixue Xiao discovered that libpng incorrectly handled certain time values.
If a user or automated system using libpng were tricked into opening a
specially crafted image, an attacker could exploit this to cause libpng to
crash, leading to a denial of service. (CVE-2015-7981)

It was discovered that libpng incorrectly handled certain small bit-depth
values. If a user or automated system using libpng were tricked into
opening a specially crafted image, an attacker could exploit this to cause
a denial of service or execute code with the privileges of the user
invoking the program. (CVE-2015-8126)