Heap-based buffer overflow in pcrecompile.c in the Perl-Compatible Regular Expression (PCRE) library 7.7 allows context-dependent attackers to cause a denial of service (crash) or possibly execute arbitrary code via a regular expression that begins with an option and contains multiple branches.

Mozilla Firefox before 2.0.0.17 and 3.x before 3.0.2, Thunderbird before 2.0.0.17, and SeaMonkey before 1.1.12 allow remote attackers to bypass cross-site scripting (XSS) protection mechanisms and conduct XSS attacks via byte order mark (BOM) characters that are removed from JavaScript code before execution, aka "Stripped BOM characters bug."