Apple's ImageIO framework contains an integer overflow vulnerability that may allow an attacker to execute code on a vulnerable system.
Graphics Interchange Format (GIF) is a popular image format supported by many Apple Mac OS X applications. The ImageIO framework allows applications to read and write various image file formats, including GIF.
From Apple Security Update 2007-003:
An integer overflow vulnerability exists in the process of handling GIF files. By enticing a user to open a maliciously-crafted image, an attacker can trigger the overflow which may lead to an unexpected application termination or arbitrary code execution. This update addresses the issue by performing additional validation of GIF files. This issue does not affect systems prior to Mac OS X v10.4.
A remote unauthenticated attacker may be able to execute arbitrary code or cause a denial-of-service condition. The specially crafted GIF file used to exploit this vulnerability may be supplied on a web page, as an email attachment or inside an email, or by some other means to convince the user into opening the malicious file.