The watch implementation in the JavaScript engine in Mozilla Firefox before 46.0, Firefox ESR 38.x before 38.8, and Firefox ESR 45.x before 45.1 allows remote attackers to execute arbitrary code or cause a denial of service (generation-count overflow, out-of-bounds HashMap write access, and application crash) via a crafted web site.
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.