CAN-2004-0990 described several more buffer overflows which had been discovered in libgd2’s PNG handling functions. However, it was determined that the update from USN-11-1 was not sufficient to prevent every possible attack, so another update is required.
If an attacker tricked a user into loading a malicious PNG image, they could leverage this into executing arbitrary code in the context of the user opening image. Most importantly, this library is commonly used in PHP. One possible target would be a PHP driven photo website that lets users upload images. Therefore this vulnerability might lead to privilege escalation to a web server’s privileges.