Use-after-free vulnerability in the mozilla::dom::HTMLMediaElement::LookupMediaElementURITable function in Mozilla Firefox before 22.0, Firefox ESR 17.x before 17.0.7, Thunderbird before 17.0.7, and Thunderbird ESR 17.x before 17.0.7 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via a crafted web site.