Heap-based buffer overflow in Mozilla Thunderbird before 2.0.0.17 and SeaMonkey before 1.1.12 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a long header in a news article, related to "canceling [a] newsgroup message" and "cancelled newsgroup messages."
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.