libpng - out of bound access

Steve Grubb discovered a problem in the Portable Network Graphics
library libpng which is utilised in several applications. When
processing a broken PNG image, the error handling routine will access
memory that is out of bounds when creating an error message.
Depending on machine architecture, bounds checking and other
protective measures, this problem could cause the program to crash if
a defective or intentionally prepared PNG image file is handled by
libpng.

This could be used as a denial of service attack against various
programs that link against this library. The following commands will
show you which packages utilise this library and whose programs should
probably restarted after an upgrade:

   apt-cache showpkg libpng2
   apt-cache showpkg libpng3

The following security matrix explains which package versions will
contain a correction.

We recommend that you upgrade your libpng and related packages.