The http-index-format MIME type parser (nsDirIndexParser) in Firefox 3.x before 3.0.4, Firefox 2.x before 2.0.0.18, and SeaMonkey 1.x before 1.1.13 does not check for an allocation failure, which allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via an HTTP index response with a crafted 200 header, which triggers memory corruption and a buffer overflow.
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.