Heap-based buffer overflow in the nsBMPEncoder::AddImageFrame function in Mozilla Firefox before 49.0, Firefox ESR 45.x before 45.4, and Thunderbird < 45.4 allows remote attackers to execute arbitrary code via a crafted image data that is mishandled during the encoding of an image frame to an image.
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.