Description
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.
Published: 2026-11-05
Score: 5.1 Medium
EPSS: n/a
KEV: No
AI Analysis

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Remediation

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History

Thu, 05 Nov 2026 19:00:00 +0000

Type Values Removed Values Added
Description 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.
Title mcp-go before v1.2.1 Origin Validation Error via Unvalidated Well-Known Protected Resource Metadata
Weaknesses CWE-346
References
Metrics cvssV3_1

{'score': 8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N'}

cvssV4_0

{'score': 5.1, 'vector': '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'}

Subscriptions

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-05T18:45:36.197Z

Reserved: 2026-11-05T18:19:12.668Z

Link: CVE-2026-123272

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-11-05T19:17:20.713

Modified: 2026-11-05T19:17:20.847

Link: CVE-2026-123272

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

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Weaknesses