CVE-2026-42559

8.8

HIGH CVSS 3.1

RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport

Overview

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.

Details

INFO

Published Date :

May 14, 2026, 3:16 p.m.

Last Modified :

June 17, 2026, 10:48 a.m.

Remotely Exploit :

Yes !

Source :

[email protected]

Impact

Affected Products

The following products are affected by CVE-2026-42559 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

No affected product recoded yet

: Total Affected Vendor : 0 | Products : 0

Scoring

CVSS Scores

The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.

Score	Version	Severity	Vector	Exploitability Score	Impact Score	Source
	CVSS					134c704f-9b21-4f2e-91b3-4a467353bcc0
	CVSS 3.1	HIGH				[email protected]

Solution

Update RMCP to version 1.4.0 or later to fix DNS rebinding vulnerability.

Update the rmcp crate to version 1.4.0 or later.
Ensure Host header validation is implemented.

Public PoC/Exploit Available at Github

CVE-2026-42559 has a 5 public PoC/Exploit available at Github. Go to the Public Exploits tab to see the list.

References

References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-42559.

URL	Resource
https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3
https://github.com/modelcontextprotocol/rust-sdk/issues/815
https://github.com/modelcontextprotocol/rust-sdk/issues/822
https://github.com/modelcontextprotocol/rust-sdk/pull/764
https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx

CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-42559 is associated with the following CWEs:

CWE-346: Origin Validation Error

CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-42559 weaknesses.

CAPEC-21: Exploitation of Trusted Identifiers Exploitation of Trusted Identifiers CAPEC-59: Session Credential Falsification through Prediction Session Credential Falsification through Prediction CAPEC-60: Reusing Session IDs (aka Session Replay) Reusing Session IDs (aka Session Replay) CAPEC-75: Manipulating Writeable Configuration Files Manipulating Writeable Configuration Files CAPEC-76: Manipulating Web Input to File System Calls Manipulating Web Input to File System Calls CAPEC-89: Pharming Pharming CAPEC-111: JSON Hijacking (aka JavaScript Hijacking) JSON Hijacking (aka JavaScript Hijacking) CAPEC-141: Cache Poisoning Cache Poisoning CAPEC-142: DNS Cache Poisoning DNS Cache Poisoning CAPEC-160: Exploit Script-Based APIs Exploit Script-Based APIs CAPEC-384: Application API Message Manipulation via Man-in-the-Middle Application API Message Manipulation via Man-in-the-Middle CAPEC-385: Transaction or Event Tampering via Application API Manipulation Transaction or Event Tampering via Application API Manipulation CAPEC-386: Application API Navigation Remapping Application API Navigation Remapping CAPEC-387: Navigation Remapping To Propagate Malicious Content Navigation Remapping To Propagate Malicious Content CAPEC-388: Application API Button Hijacking Application API Button Hijacking CAPEC-510: SaaS User Request Forgery SaaS User Request Forgery CAPEC-73: User-Controlled Filename User-Controlled Filename CAPEC-89: Pharming Pharming CAPEC-142: DNS Cache Poisoning DNS Cache Poisoning CAPEC-275: DNS Rebinding DNS Rebinding

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

tomtom215/mcp-conformance

None

Rust

Updated: 2 weeks, 1 day ago

0 stars 0 fork 0 watcher

Born at : June 9, 2026, 6:48 p.m. This repo has been linked 1 different CVEs too.

codeverseproo/mcp-security-kit

Production security middleware for MCP servers - DNS rebinding protection, CORS guard, tool filtering

Python TypeScript

Updated: 2 months ago

0 stars 0 fork 0 watcher

Born at : May 30, 2026, 4:08 p.m. This repo has been linked 7 different CVEs too.

mcp-security-project/mcp-cve-project

The Project shares all information on MCP related CVE's published

mcp mcp-security mcp-cve

Updated: 2 weeks, 3 days ago

19 stars 4 fork 4 watcher

Born at : May 7, 2026, 3:47 p.m. This repo has been linked 307 different CVEs too.

studiomeyer-io/mcp-armor

Drop-in Rust sidecar for MCP servers — scans tool calls for prompt injection, validates Ed25519 manifest signatures, blocks marketplace-poisoning vectors. <5ms p99 overhead. Defense against OX Security MCP advisory (10+ CVEs, April 2026).

anthropic built-in-mallorca claude ed25519 mcp mcp-security mcp-server model-context-protocol prompt-injection rust security sidecar signature supply-chain-security

Rust Dockerfile

Updated: 2 weeks, 2 days ago

1 stars 0 fork 0 watcher

Born at : May 3, 2026, 9:49 p.m. This repo has been linked 11 different CVEs too.

holmanholdings/lionguard

Cathedral-Grade Security for AI Agents. Attack vectors updated daily. Local-first, zero API cost. MIT licensed.

Python

Updated: 2 weeks ago

6 stars 0 fork 0 watcher

Born at : March 13, 2026, 5:10 p.m. This repo has been linked 119 different CVEs too.

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-42559 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-42559 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

CVE Modified by [email protected]

Jun. 17, 2026

Action	Type	Old Value	New Value
Added	Affected		[{'vendor': 'modelcontextprotocol', 'product': 'rust-sdk', 'versions': [{'status': 'affected', 'version': '< 1.4.0'}]}]

CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0