PT-2026-137683

CVE-2026-123272

Published

2026-11-05

Updated

2026-11-05

Description by

CVSS 3.1

8.0

High

MetricsAV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

Name of the Vulnerable Software and Affected Versions Mark3labs mcp-go versions prior to 1.2.1

Description Improper validation in the fetchServerMetadata() function of the OAuthHandler allows malicious MCP servers to obtain tokens for unauthorized resources. By declaring arbitrary resources in well-known metadata, an attacker can specify a different MCP server as the RFC 8707 resource indicator, leading the authorization server to issue tokens that the attacker can then replay against that resource.

Recommendations Update Mark3labs mcp-go to version 1.2.1 or later.

Exploitability

Exploit

Fix

Impacts

Researchers

Ed Zynda

Theodoros Lampropoulos

Vendors

Affected products

Weakness enumeration

CWE-346: Origin Validation Error