On December 10, Canonical published in a security notice details about a GIMP vulnerability for its Ubuntu 12.10 Ubuntu 12.04, Ubuntu 11.10, and Ubuntu 10.04 LTS operating systems.
According to Canonical, GIMP could have been made to crash or run programs as the user’s login, if it opened a specially crafted file.
It was discovered that GIMP incorrectly handled malformed XWD files. If a user were tricked into opening a specially crafted XWD file, an attacker could have caused GIMP to crash, or possibly execute arbitrary code, with the user's privileges.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can simply fix the security flaws by upgrading the operating systems to the latest gimp package, specific to each distribution.
A normal system update, executed with the Update Manager, will implement all the necessary changes. A complete system restart is not necessary.