MEDIUM 5.1 NVD
CVE-2026-123272
Mark3labs mcp-go before v1.2.1 contains an improper validation vulnerability in OAuthHandler.fetchServerMetadata that allows malicious MCP servers to obtain tok
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.
References
- https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/t
- https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443
- https://github.com/mark3labs/mcp-go/pull/1053
- https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1
- https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx
This medium severity vulnerability with a CVSS score of 5.1 was published on 2026-11-05 via NVD.
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