Multiple buffer underflows in the base64 decoder in base64.c in (1) bogofilter and (2) bogolexer in bogofilter before 1.2.2 allow remote attackers to cause a denial of service (heap memory corruption and application crash) via an e-mail message with invalid base64 data that begins with an = (equals) character.
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.