CVE-2026-42559

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 products

Dynoxide, Rmcp

Fix

Available

CVSS 3.1

8.8 HIGH

EPSS

0.2% (12th percentile)

Weakness

CWE-350, CWE-346

NVD status

Deferred

Published

2026-05-14