mcp-go OAuth client accepts unvalidated resource from metadata

An AI connection development library can leak logins to other services.

Summary

The OAuth client in mcp-go does not validate the resource declared in well-known metadata, so a malicious MCP server can get access tokens for other resources. Versions v0.48.0 through v1.2.0 are affected.

Affected when

Use of mcp-go's OAuth client transport
Connection to a malicious or compromised MCP server

What to do

Update to v1.2.1.

Products and platforms

mark3labs mcp-go

CVE IDs

CVE-2026-123272 (opens in a new tab)

Sources

Advisory: github.com (opens in a new tab) · github.com (opens in a new tab)
Write-up: github.com (opens in a new tab) · vulncheck.com (opens in a new tab)
CVE record: cve.org (opens in a new tab)

Times

First published 2026-11-05 18:45 UTC

First seen 2026-11-09 17:00 UTC