Vulnerability Instance

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.