The scriptfu network server in GIMP 2.6 does not require authentication, which allows remote attackers to execute arbitrary commands via the python-fu-eval command.
https://security.gentoo.org/glsa/201603-01
http://www.xerox.com/download/security/security-bulletin/16287-4d6b7b0c81f7b/cert_XRX13-003_v1.0.pdf
http://www.reactionpenetrationtesting.co.uk/GIMP-scriptfu-python-command-execution.html
http://www.openwall.com/lists/oss-security/2012/08/20/1
http://www.openwall.com/lists/oss-security/2012/08/17/2
http://www.openwall.com/lists/oss-security/2012/08/16/6
http://archives.neohapsis.com/archives/bugtraq/2012-08/0106.html