Mooncake transfer engine: Denial of service via P2P handshake daemon

Summary

Mooncake transfer engine up to version 0.3.13.post1 contains a denial-of-service vulnerability in its P2P handshake daemon. An unauthenticated remote attacker who can reach the handshake RPC port can send a metadata request and never read the reply, which blocks the single listener thread. This stalls all subsequent handshakes, metadata fetches, notify and probe requests until the engine process is restarted. The attack is rated high complexity and requires specific deployment conditions.

Affected

• kvcache-ai Mooncake transfer engine, versions 0 up to and including 0.3.13.post1
• Python package mooncake-transfer-engine
• Default configuration: unaffected per CNA record (affected range as listed by VulnCheck)

Fixed in

• Unknown. A fix is reported on the main branch (PR #4451), but no release containing it has been confirmed.
• A partial fix may not fully address the report (see PR #5051 discussion).

Workaround

• Restrict access to the handshake RPC port, the data port and the HTTP metadata server to the deployment's own hosts only.
• Restrict the whole Mooncake port range (documented 15000-17000), since --mooncake-port is not used by the engine.
• Restart the engine process to recover after an attack.

Exploitation

• Publicly disclosed in the GitHub issue #4443.
• SSVC assessment: PoC available, not automatable.
• No public exploit code confirmed; not listed in CISA KEV as of the research date.

Our recommendation

• Check whether Mooncake is installed (pip list, container images, AI serving stacks such as SGLang or vLLM).
• If present, restrict the handshake, data and metadata ports to the cluster network.
• Monitor the Mooncake releases page and update as soon as a fixed release is published.
• Treat the risk as high if the ports are reachable beyond the cluster, moderate if internal only.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• Mooncake GitHub repository github.com
• Mooncake issue #4443 github.com
• VulnCheck advisory www.vulncheck.com
• Mooncake issue #4626 github.com
• Mooncake fix PR #4451 github.com
• Mooncake PR #5051 github.com
• mstar issue #466 github.com
• Strix CVE record www.strix.ai

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 17:34.