Decoding a negative signed 64-bit integer modifies the corresponding bytes in the caller-provided input buffer. Applications that retain or reuse encoded input for integrity checks, logging, or subsequent processing may observe silently corrupted data.

Positive integers and other MessagePack value types are not affected.

The decoder now computes signed 64-bit values without writing to the input buffer.

Copy untrusted MessagePack input before decoding it, or do not retain or reuse input buffers after decoding.