CVE-2026-42559CWE-346CWE-350

RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

High · published May 14, 2026

CVSS v3.1
8.8
EPSS
0%
Percentile
14.5
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
8.8 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00242 · 14.5th percentile
Weaknesses
CWE-346 · Origin Validation Error; CWE-350 · Reliance on Reverse DNS Resolution for a Security-Critical Action
Published
2026-05-14T14:24Z
EPSS history
Timeline
  • 14 MAY 14:24Z
    RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport
    cvelistv5