CVE-2026-123272 – mcp-go before v1.2.1 Origin Validation Error via Unvalidated Well-Known Protected Resource Metadata

​CVE ID :CVE-2026-123272

Published : Nov. 5, 2026, 6:45 p.m. | 43 minutes ago

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.

Severity: 8.0 | HIGH

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