The Content Security Policy (CSP) implementation in Mozilla Firefox 4.x through 12.0, Firefox ESR 10.x before 10.0.5, Thunderbird 5.0 through 12.0, Thunderbird ESR 10.x before 10.0.5, and SeaMonkey before 2.10 does not block inline event handlers, which makes it easier for remote attackers to conduct cross-site scripting (XSS) attacks via a crafted HTML document.