Buffer overflow in JavaScript atom map — Mozilla

Security researcher Christian Holler reported that the JavaScript engine’s internal mapping of string values contained an error in cases where the number of values being stored was above 64K. In such cases an offset pointer was manually moved forwards and backwards to access the larger address space. If an exception was thrown between the time that the offset pointer was moved forward and the time it was reset, then the exception object would be read from an invalid memory address, potentially executing attacker-controlled memory.