CVE-2026-42559

RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.

Affected

modelcontextprotocol · rust-sdk

CVSS v3.1 GITHUB

8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS

0.24% chance of exploitation in the next 30 days, 14th percentile

Published

2026-05-14

Proof-of-concept exploits (1)

• joaovicdev/EXPLOIT-CVE-2026-42559/blob/77bfc3623d51f5e5fd3b8e97cd7e2e8107a1d1cf/exploit/e…0★ · 2026-09-06

Security advisories

• advisories/GHSA-89vp-x53w-74fx

References

• CVE Record
• NVD entry

Related

• CVE-2021-44228
• CVE-2025-27515
• CVE-2025-55182
• CVE-2026-22778
• CVE-2026-23958
• CVE-2026-26216