---
title: "CVE-2026-63127: RMCP - Authentication Bypass"
description: "RMCP Rust SDK < 2.0.0 contains an OAuth authorization bypass caused by omission of RFC 9728 resource field validation in ResourceServerMetadata, letting malicious MCP servers impersonate victims by capturing access tokens, exploit requires victim to complete authorization flow."
url: https://panop.io/threat-heartbeat/CVE-2026-63127/
---

# CVE-2026-63127 RMCP - Authentication Bypass

RMCP Rust SDK < 2.0.0 contains an OAuth authorization bypass caused by omission of RFC 9728 resource field validation in ResourceServerMetadata, letting malicious MCP servers impersonate victims by capturing access tokens, exploit requires victim to complete authorization flow.

CVSS base score 8.2 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.20% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-63127)

## Details

Type

Authentication Bypass

Impact

Broken Authentication

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

Published

16 September 2026

Updated

15 October 2026

Weakness

[CWE-345](https://cwe.mitre.org/data/definitions/345.html)

## Vendor fix

Upgrade to version 2.0.0 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-63127](https://nvd.nist.gov/vuln/detail/CVE-2026-63127)
- [https://github.com/modelcontextprotocol/rust-sdk/commit/c1a8b29ff2cc45e7820b900dae42cbb4958089ec](https://github.com/modelcontextprotocol/rust-sdk/commit/c1a8b29ff2cc45e7820b900dae42cbb4958089ec)
- [https://github.com/modelcontextprotocol/rust-sdk/pull/937](https://github.com/modelcontextprotocol/rust-sdk/pull/937)
- [https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0](https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0)
- [https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj](https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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