CVE 2012-3966
Mozilla Firefox before 15.0, Firefox ESR 10.x before 10.0.7, Thunderbird before 15.0, Thunderbird ESR 10.x before 10.0.7, and SeaMonkey before 2.12 allow remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a negative height value in a BMP image within a .ICO file, related to (1) improper handling of the transparency bitmask by the nsICODecoder component and (2) improper processing of the alpha channel by the nsBMPDecoder component.
See the 
CVE page on Mitre.org
for more details.
