Mooncake Transfer Engine EUVD-2026-91134

Exploitation requires network reachability to Mooncake's P2P handshake RPC port (the SocketHandShakePlugin listener). The attacker sends a Metadata request and then refuses to read the server's reply, exploiting the design in which a single listener thread performs a blocking writeFully() - so one slow/non-reading client stalls that thread and blocks all handshakes, metadata fetches, notify and probe operations. No authentication is required (PR:N) and no user interaction is needed (UI:N), but the practical limiting factors are: the handshake RPC port must be exposed to untrusted clients (deployments that bind it to a trusted internal network/loopback are not remotely exploitable), and the attack reduces to availability loss only - it grants no code execution, data disclosure, or integrity impact. The AC:H/AT:P metrics indicate the stall depends on hitting the blocking-write state rather than a single guaranteed trigger.

This is a genuine availability-focused issue but not a drop-everything emergency. The CVSS 4.0 vector (AV:N/AC:H/AT:P/PR:N/UI:N) scores 8.2 (High) driven entirely by VA:H - a complete denial of service of the handshake daemon - with zero confidentiality or integrity impact (VC:N/VI:N/VA:H). The unauthenticated network reachability (PR:N, AV:N) raises concern, but AC:H and AT:P signal that reliable exploitation carries meaningful conditions: the attacker must successfully stall the single listener thread inside writeFully(), which implies some timing/race or resource-state dependency rather than a trivial one-shot crash. There is no CISA KEV listing and no public exploit identified at time of analysis, so the 8.2 is a theoretical-severity figure, not evidence of real-world weaponization. Signals are internally consistent (network DoS, no data impact), so there are no contradictions to flag; the main caveat is that the attack-complexity/requirement metrics indicate this is less push-button than the headline score suggests. Priority should be driven by whether Mooncake's handshake RPC port is network-exposed in a given deployment - if it is reachable by untrusted clients, treat as a real availability risk to the LLM inference/KV-cache fabric.

An attacker with network reach to a Mooncake transfer-engine node's handshake RPC port opens a connection and sends a Metadata request but then deliberately never reads the reply, causing SocketHandShakePlugin's single listener thread to block indefinitely in writeFully(). With that lone thread stalled, all subsequent handshakes, metadata fetches, notify and probe requests are broken, degrading or halting the distributed KV-cache transfer service. No public exploit code is identified, but the technique is simple to reproduce for anyone who can reach the port.