Off-by-one error in the QUtf8Decoder::toUnicode function in Trolltech Qt 3 allows context-dependent attackers to cause a denial of service (crash) via a crafted Unicode string that triggers a heap-based buffer overflow. NOTE: Qt 4 has the same error in the QUtf8Codec::convertToUnicode function, but it is not exploitable.
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.