CVE-2026-42559 | BDVDB-2026-333346 Detail

modelcontextprotocolrust-sdk

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.

Impact#

Per CVSS v3.1: confidentiality impact high, integrity impact high, availability impact high. Attack vector: network.

Weaknesses#

CWE-346 Origin Validation Error
CWE-350 Reliance on Reverse DNS Resolution for a Security-Critical Action

References#

Exploit#

No public exploit known

History#

Version 12026-05-14Record published in the CVE List.

Published

Published: 2026-05-14
Last modified: 2026-05-14

Vendor information

Vendor: modelcontextprotocol
Product: rust-sdk

All modelcontextprotocol vulnerabilities

Score

8.8 High

EPSS

less than 1%, Very Low

Estimated chance of exploitation in the next 30 days. EPSS percentile: 19.2.

KEV

Not listed in the CISA Known Exploited Vulnerabilities catalog.

Impact

Not classified

Action

No specific action is recorded in the source data. Check the references for vendor guidance.

Affected Systems

Vulnerable
< 1.4.0
Fixed
Not stated

Scoring System

CVSS v4.0

Not available

CVSS v3.1

8.8 High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Metric breakdown
Attack Vector	Network
Attack Complexity	Low
Privileges Required	None
User Interaction	Required
Scope	Unchanged
Confidentiality	High
Integrity	High
Availability	High

CVSS v3.0

Not available

CVSS v2

Not available

Source: CVE List v5 (record); CISA KEV (kev, action); FIRST EPSS (epss).