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CVE-2026-42559

8.8 · HIGH

RMCP is an official Rust SDK for the Model Context Protocol.

Published May 14, 2026CWE-346EPSS 0.24%

Overview

CVE-2026-42559 is a high-severity vulnerability. It was published on May 14, 2026 and has a CVSS 3.1 base score of 8.8 (HIGH).

This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3GitHubgithub.com/modelcontextprotocol/rust-sdk/issues/815GitHubgithub.com/modelcontextprotocol/rust-sdk/issues/822GitHubgithub.com/modelcontextprotocol/rust-sdk/pull/764GitHubgithub.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx

How CyberStrike helps

Frequently asked questions

What is CVE-2026-42559?

CVE-2026-42559 is a high-severity vulnerability. It was published on May 14, 2026 and has a CVSS 3.1 base score of 8.8 (HIGH).

How severe is CVE-2026-42559?

This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-42559?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-42559?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-42559 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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