CVE-2026-42559 | THREATINT

Description

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.

PUBLISHED Reserved 2026-04-28 | Published 2026-05-14 | Updated 2026-05-14 | Assigner GitHub_M

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

Problem types

CWE-346: Origin Validation Error

CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action

Product status

< 1.4.0

affected

References

github.com/...st-sdk/security/advisories/GHSA-89vp-x53w-74fx

github.com/modelcontextprotocol/rust-sdk/issues/815

github.com/modelcontextprotocol/rust-sdk/issues/822

github.com/modelcontextprotocol/rust-sdk/pull/764

github.com/...ommit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3

cve.org (CVE-2026-42559)

nvd.nist.gov (CVE-2026-42559)

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