Summary
msgpack5: Reserved byte can cause unbounded stream buffering
Advisory details
Impact
The reserved MessagePack byte 0xc1 is incorrectly treated as incomplete input. When it appears at the start of a decoder stream, all subsequent data is retained while the decoder waits for bytes that can never make the value valid, allowing memory exhaustion.
Patches
The decoder now rejects 0xc1 as invalid input. Streaming decoders release buffered input and stop after unrecoverable decoding errors.
Workarounds
Reject 0xc1 before streaming input to msgpack5, and enforce stream byte and time limits.
References
Related vulnerabilities
All Supply chain →- CRITICALCVE-2026-9205
Langflow: Weak Fernet Key via random.seed()
- HIGHCVE-2026-96627
Arcane: Delegated users:update permission allows admin account takeover via password reset (no privilege-hierarchy check)
- MEDIUMCVE-2026-96628
Arcane: Environment access token bypasses the admin-required authorization gate on `/api/debug/pprof`
- CRITICALCVE-2026-105192
LMCache: Remote code execution via unsafe deserialization in multiprocess mode transport
- HIGHCVE-2026-100349
kin-openapi openapi3filter: nil-pointer panic in ValidateResponse on a response header declared with content
- MEDIUMCVE-2026-58494
Wasmtime: WASI hard links bypass wasmtime-wasi's FilePerms for destination