CVE-2026-42559

PoC —

CVSS 3.1

8.8 high

EPSS

<1%p12

Published

May 14, 2026 (May 14, 2026)

Modified

Jun 17, 2026

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.

Weakness: CWE-346, CWE-350
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

NVD CVE.org GitHub PoCs EPSS (0.2%)

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