gcdRadar
archive/Patch now/AIR-2026-1075
closedclosed 14 May 2026Patch now2 Disclosed vulnerabilityAI

CVE-2026-42559: RMCP Streamable HTTP Server Host Header Validation Flaw

RMCP, Model Context Protocol

Prior to version 1.4.0, the RMCP crate's Streamable HTTP server transport lacked Host header validation, permitting DNS rebinding attacks. This allowed malicious websites to send authenticated requests to local or private MCP servers.

disclosed CVENo confirmed exploitation, so this record is tracked as a disclosed vulnerability and not counted as an incident. It moves into the counts if CISA or the vendor confirms exploitation. Why

CVSS
8.8
EPSS
<0.01 · top 81% · 2026-11-13
EPSS scores by FIRST
fix status
Fix status unknown
first report
14 May 2026
last update
14 May 2026
CVE ids
CVE-2026-42559other records

Timeline · 1

  1. 14 May 2026CVE-2026-42559: RMCP is an official Rust SDK for the Model Context Protocol.

Sources · 1

Advisories and databases

  1. 2026-05-14
    CVE-2026-42559: RMCP is an official Rust SDK for the Model Context Protocol.
    NVD · nvd.nist.gov/vuln/detail/CVE-2026-42559

Titles and links belong to their publishers. The summary above is written by gcdRadar in its own words; data is CC BY-SA 4.0.

Classification

lane
Patch now
AI role
Attack on AI
categories
Infrastructure vulnerability
severity
2 · Disclosed vulnerability
fix status
Fix status unknown
targets
Framework / tooling
owasp llm top 10
LLM03:2025 Supply Chain
mitre atlas
no technique for these categories
tags
dns-rebindingmodel-context-protocol
dates
happened 14 May 2026 · first reported 14 May 2026
origin
NVD
Vulnerability record from NVD / the GitHub Advisory Database. This product uses the NVD API but is not endorsed or certified by the NVD.
record
confidence 0.90 · created 2026-10-18 10:04Z · updated 2026-10-18 10:04Z

Lane, AI role, categories and severity come from the classifier; the OWASP and ATLAS rows are derived from the categories. How these are assigned

Copy a brief

This record as a short Markdown brief, for a ticket, a chat or a coding agent.

the brief as text
# CVE-2026-42559: RMCP Streamable HTTP Server Host Header Validation Flaw

https://gcdradar.vercel.app/incidents/cve-2026-42559-rmcp-streamable-http-server-host-header-valid · AIR-2026-1075 · closed 2026-05-14

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2026-05-14
- AI role: Attack on AI
- Products: RMCP, Model Context Protocol
- CVE ids: CVE-2026-42559
- CVSS: 8.8

## Summary

Prior to version 1.4.0, the RMCP crate's Streamable HTTP server transport lacked Host header validation, permitting DNS rebinding attacks. This allowed malicious websites to send authenticated requests to local or private MCP servers.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2026-05-14: CVE-2026-42559: RMCP is an official Rust SDK for the Model Context Protocol. (https://nvd.nist.gov/vuln/detail/CVE-2026-42559)

## Sources

- 2026-05-14 NVD: CVE-2026-42559: RMCP is an official Rust SDK for the Model Context Protocol. https://nvd.nist.gov/vuln/detail/CVE-2026-42559

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.

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