Heap-based buffer overflow in Mozilla Thunderbird before 2.0.0.12 and SeaMonkey before 1.1.8 might allow remote attackers to execute arbitrary code via a crafted external-body MIME type in an e-mail message, related to an incorrect memory allocation during message preview.
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.