{"id":"CVE-2026-123272","published":"2026-11-05T19:17:20.713","lastModified":"2026-11-05T21:18:45.960","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.","cvssScore":8,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N","cwes":["CWE-346"],"vendors":[],"products":[],"references":[{"url":"https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.go#L799-L821","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/pull/1053","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx","tags":[]},{"url":"https://www.vulncheck.com/advisories/mcp-go-before-1.2.1-origin-validation-error-via-unvalidated-well-known-protected-resource-metadata","tags":[]}],"exploitRefs":[{"url":"https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.go#L799-L821","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/pull/1053","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1","tags":[]},{"url":"https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx","tags":[]}],"hasPoc":true,"ai":null}