Cyber Resilience

CVE-2026-42559

High

Published: 14 May 2026

Published
14 May 2026
Modified
14 May 2026
KEV Added
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Patch
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CVSS Score v3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS Score 0.0021 11.6th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-42559 is a high-severity Origin Validation Error (CWE-346) vulnerability. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 11.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

This vulnerability is AI-related — categorised as AI Agent Protocols and Integrations; in the Protocol-Specific Risks risk domain.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability details

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…

more

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.

CWE(s)
CWE-346CWE-350

AI Security AnalysisAI

AI Category
AI Agent Protocols and Integrations
Risk Domain
Protocol-Specific Risks
OWASP Top 10 for LLMs 2025
None mapped
Classification Reason
Matched keywords: mcp, model context protocol

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Why these techniques?

Missing Host header validation enables DNS rebinding from a malicious site to reach and interact with the local/private MCP HTTP server, directly facilitating exploitation of a network-accessible application (T1190).

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-6508Shared CWE-346
CVE-2025-1102Shared CWE-346
CVE-2025-21511Shared CWE-346
CVE-2026-22794Shared CWE-346
CVE-2026-1490Shared CWE-350
CVE-2024-8487Shared CWE-346
CVE-2024-10956Shared CWE-346
CVE-2026-41057Shared CWE-346
CVE-2026-6662Shared CWE-346
CVE-2025-25306Shared CWE-346

Affected Assets

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

IA-9 Service Identification and Authentication
addresses: CWE-346

Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.

SC-11 Trusted Path
addresses: CWE-346

Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.

SC-20 Secure Name/Address Resolution Service (Authoritative Source)
addresses: CWE-346

Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.

SC-21 Secure Name/Address Resolution Service (Recursive or Caching Resolver)
addresses: CWE-346

Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.

SC-23 Session Authenticity
addresses: CWE-346

Mandates origin validation so that only legitimate endpoints can continue the authenticated session.

References