The IonMonkey JavaScript engine in Mozilla Firefox before 24.0, Thunderbird before 24.0, and SeaMonkey before 2.21, when Valgrind mode is used, does not properly initialize memory, which makes it easier for remote attackers to obtain sensitive information via unspecified vectors.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.