---
id: CVE-2026-63127
title: RMCP is an official Rust SDK for the Model Context Protocol
summary: >-
  RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0,
  the rmcp crate's OAuth implementation in crates/rmcp/src/transport/auth.rs
  omits the RFC 9728 resource field from ResourceServerMetadata and allows
  discover_oau…
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N'
cwe:
  - CWE-345
  - CWE-289
vendor: modelcontextprotocol
product: rust-sdk
affected:
  - rust-sdk < 2.0.0
published: '2026-09-16'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T16:17:14.323'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63127'
references:
  - url: >-
      https://github.com/modelcontextprotocol/rust-sdk/commit/c1a8b29ff2cc45e7820b900dae42cbb4958089ec
    label: security-advisories@github.com
  - url: 'https://github.com/modelcontextprotocol/rust-sdk/pull/937'
    label: security-advisories@github.com
  - url: 'https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj
    label: security-advisories@github.com
  - url: >-
      https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63127.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-63127'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2535503'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-63127'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63127'
  - url: 'https://github.com/advisories/GHSA-33f5-2c5q-wgwj'
  - url: 'https://github.com/modelcontextprotocol/rust-sdk'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
  - ghsa
  - rust
  - osv
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-16T15:38:50.771703Z'
ingestedAt: '2026-09-16T14:57:28.031Z'
aliases:
  - GHSA-33f5-2c5q-wgwj
ecosystem: rust
patched:
  - rmcp 2.0.0
epss: 0.00195
epssPercentile: 0.09503
---

## Overview

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's OAuth implementation in crates/rmcp/src/transport/auth.rs omits the RFC 9728 resource field from ResourceServerMetadata and allows discover_oauth_server_via_resource_metadata to use protected-resource metadata without confirming that the returned resource identifier exactly matches the configured MCP server. A malicious MCP server can publish metadata for a different legitimate MCP resource and its authorization server, causing a victim who connects and completes the authorization flow to obtain a legitimate access token that the client subsequently sends to the malicious server. The attacker can capture the token and impersonate the victim against the legitimate MCP resource within the token's granted scopes. This issue is fixed in version 2.0.0.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · updated 2026-09-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63127.json)

## Package advisory (CVE-2026-63127)

Affected packages:

- `rmcp < 2.0.0`

Patched in:

- `rmcp 2.0.0`

Source: https://github.com/advisories/GHSA-33f5-2c5q-wgwj