yaSSL 1.7.5 and earlier, as used in MySQL and possibly other products, allows remote attackers to cause a denial of service (crash) via a Hello packet containing a large size value, which triggers a buffer over-read in the HASHwithTransform::Update function in hash.cpp.
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.