Remote code execution by overflowing CSS reference counter — Mozilla

An anonymous researcher, via TippingPoint’s Zero Day Initiative program, reported a vulnerability in Mozilla’s internal CSSValue array data structure. The vulnerability was caused by an insufficiently sized variable being used as a reference counter for CSS objects. By creating a very large number of references to a common CSS object, this counter could be overflowed which could cause a crash when the browser attempts to free the CSS object while still in use. An attacker could use this crash to run arbitrary code on the victim’s computer.