{"affected":[{"defaultStatus":"unaffected","ecosystem":"golang","packageName":"github.com/mark3labs/mcp-go","product":"mcp-go","source":"CNA: VulnCheck","vendor":"mark3labs","versions":[{"lessThan":"v1.2.1","status":"affected","version":"v0.48.0","versionType":"semver"}]}],"cveId":"CVE-2026-123272","cwes":["CWE-346"],"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.","epss":null,"exploits":[],"kev":null,"metrics":[{"score":5.1,"severity":"medium","source":"CNA: VulnCheck","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","version":"4.0"},{"score":8,"severity":"high","source":"CNA: VulnCheck","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N","version":"3.1"}],"modifiedAt":1793912512297,"publishedAt":1793904336197,"references":[{"source":"CNA: VulnCheck","tags":["vendor-advisory"],"url":"https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx"},{"source":"CNA: VulnCheck","tags":["issue-tracking","patch"],"url":"https://github.com/mark3labs/mcp-go/pull/1053"},{"source":"CNA: VulnCheck","tags":["patch"],"url":"https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443"},{"source":"CNA: VulnCheck","tags":["release-notes"],"url":"https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.go#L799-L821"},{"source":"CNA: VulnCheck","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/mcp-go-before-1.2.1-origin-validation-error-via-unvalidated-well-known-protected-resource-metadata"}],"remediation":[{"kind":"fix","source":"CNA: VulnCheck","text":"The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.","url":"https://github.com/mark3labs/mcp-go/pull/1053"},{"kind":"fix","source":"CNA: VulnCheck","text":"The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.","url":"https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443"}],"revision":"50eb9b6f5c664710bedce1d454a6924859436d911e9a4d643b8b8c18c7f5f5a2","sources":[{"modifiedAt":1793912512297,"name":"CNA: VulnCheck","retrievedAt":1793913810140,"url":"https://www.cve.org/CVERecord?id=CVE-2026-123272"}],"ssvc":{"assessedAt":1793912503498,"automatable":"no","exploitation":"none","source":"ADP: CISA-ADP","technicalImpact":"total"},"status":"published","title":"mcp-go before v1.2.1 Origin Validation Error via Unvalidated Well-Known Protected Resource Metadata","updatedAt":1793913810140}