Golioth Firmware SDK < 0.22.0 Payload Utils Stack-based Buffer Overflow

Golioth Firmware SDK version 0.10.0 prior to 0.22.0, fixed in commit 48f521b, contain a stack-based buffer overflow in Payload Utils. The golioth_payload_as_int() and golioth_payload_as_float() helpers copy network-supplied payload data into fixed-size stack buffers using memcpy() with a length derived from payload_size. The only length checks are guarded by assert(); in release builds, the asserts are compiled out and memcpy() may copy an unbounded payload_size. Payloads larger than 12 bytes (int) or 32 bytes (float) can overflow the stack, resulting in a crash/denial of service. This is reachable via LightDB State on_payload with a malicious server or MITM.