Buffer underflow in libjar in Mozilla Firefox before 42.0 and Firefox ESR 38.x before 38.4 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted ZIP archive.
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.