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Vulnerability · Published May 14, 2026 · Assigned by GitHub_M

CVE-2026-42559RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

High 8.8

In plain English

A high-severity security flaw in rust-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.8High
Exploit odds (30 days)0.3%top 80.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack tooling1Public PoC

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npmdynoxide0.9.13GHSA-fvh2-gm75-j4j7

Affected products (as reported)

VendorProductVersions
modelcontextprotocol rust-sdk < 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

References