The XrayWrapper implementation in Mozilla Firefox before 23.0 and SeaMonkey before 2.20 does not properly address the possibility of an XBL scope bypass resulting from non-native arguments in XBL function calls, which makes it easier for remote attackers to conduct cross-site scripting (XSS) attacks by leveraging access to an unprivileged object.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.