CVE-2026-42559
Published:May 14, 2026
Updated:May 18, 2026
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
https://github.com/modelcontextprotocol/rust-sdk.git (GITHUB):
Affected version(s) >=rmcp-v0.2.0 <rmcp-v1.4.0Fix Suggestion:
Update to version rmcp-v1.4.0rmcp (RUST):
Affected version(s) >=0.1.0 <1.4.0Fix Suggestion:
Update to version 1.4.0rmcp (RUST):
Affected version(s) >=0.1.0 <1.4.0Fix Suggestion:
Update to version 1.4.0Related Resources (13)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
8.8
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
EPSS
Base Score:
0.02