RMCP — Vulnerability (CVE-2026-42559)
Date: 2026-05
Attack vector: other
Category: vulnerability-disclosure
Severity: Critical
CVE: CVE-2025-64443
CVE-2026-42559
CWE: CWE-346
CWE-350
CWE-749
CVSS: 8.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H)

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.


Mitigations:

Architectural layers (MAESTRO):