CVE-2026-123272 (GCVE-0-2026-123272)

Vulnerability from cvelistv5 – Published: 2026-11-05 18:45 – Updated: 2026-11-05 21:01
VLAI
Title
mcp-go before v1.2.1 Origin Validation Error via Unvalidated Well-Known Protected Resource Metadata
Summary
Mark3labs mcp-go before v1.2.1 contains an improper validation vulnerability in OAuthHandler.fetchServerMetadata that allows malicious MCP servers to obtain tokens for other resources by declaring arbitrary resources in well-known metadata. Attackers can declare a different MCP server as the RFC 8707 resource indicator, causing the authorization server to mint tokens the attacker replays against that resource.
Severity
5.1 (Medium)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
8 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-11-05 21:01 UTC
CWE
  • CWE-346 - Origin Validation Error
Assigner
VulnCheck CNA under the mitre root
CNA scorecard B 84/100 over 7427 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
mark3labs mcp-go Affected: v0.48.0 , < v1.2.1 (semver)
guessed Create a notification for this product.
Date Public
2026-10-09 00:00
Credits
Theodoros Lampropoulos Ed Zynda (ezynda3)
Show details on NVD website
To clipboard 

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