GHSA-h72h-ppcx-998p: Zebra has pre-handshake buffer capacity reservation based on attacker-claimed body length

The P2P codec’s Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter’s PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra’s existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.