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HIGHCVE-2026-42559Published Modified CNA GitHub_M

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.

Metrics

CVSS v3.1
8.8
Severity
HIGH
Fixed in
—
Affected Products
1
Affected packages
  • modelcontextprotocol / rust-sdk
    < 1.4.0
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References