{"id":"EUVD-2026-8792","revision":null,"records":[{"revision":"6d6f216b7ad84071b44ef8f8c11c11eb","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-27896","aliases":[],"title":"MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity","description":"The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:\"method\" would also match \"Method\", \"METHOD\", etc. This violated the JSON-RPC 2.0 specification, which defines exact field names. A malicious MCP peer may have been able to send protocol messages with non-standard field casing that the SDK would silently accept. This had the potential for bypassing intermediary inspection and coss-implementation inconsistency. Go's standard JSON unmarshaling was replaced with a case-sensitive decoder in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.","state":0,"publishedAt":"2026-02-26T00:47:46.967+00:00","modifiedAt":"2026-09-16T12:04:21.685+00:00","affected":[{"ecosystem":"Vendor product","name":"go-sdk","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"modelcontextprotocol\",\n                    \"product\": \"go-sdk\",\n                    \"versions\": [\n                        {\n                            \"version\": \"< 1.3.1\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","score":7,"severity":"HIGH"}],"references":["https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f","https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-27896","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-27896","identifiers":["CVE-2026-27896"]},"retained":false,"historicalAffected":[]},{"revision":"75ef4f9bde2d45e4a0555da16fc6db53","observedAt":"2026-11-12T03:03:01.553+00:00","statement":{"source":"euvd","id":"EUVD-2026-8792","aliases":["CVE-2026-27896","GHSA-wvj2-96wp-fq3f"],"title":"The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged …","description":"The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:\"method\" would also match \"Method\", \"METHOD\", etc. This violated the JSON-RPC 2.0 specification, which defines exact field names. A malicious MCP peer may have been able to send protocol messages with non-standard field casing that the SDK would silently accept. This had the potential for bypassing intermediary inspection and coss-implementation inconsistency. Go's standard JSON unmarshaling was replaced with a case-sensitive decoder in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","score":7,"severity":null}],"references":["https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f","https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-8792","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Feb 26, 2026, 12:47:46 AM","dateUpdated":"Sep 16, 2026, 12:04:21 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. 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Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-27896","identifiers":["CVE-2026-27896"]},"retained":false,"historicalAffected":[]},{"revision":"6c46ee7bdadd400bbd1f4ffb854da50e","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-wvj2-96wp-fq3f","aliases":["CVE-2026-27896","GO-2026-4569"],"title":"MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity","description":"The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:\"method\" would also match \"Method\", \"METHOD\", etc. Additionally, Go's standard library folds the Unicode characters ſ (U+017F) and K (U+212A) to their ASCII equivalents s and k, meaning fields like \"paramſ\" would match \"params\". This violated the JSON-RPC 2.0 specification, which defines exact field names.\n\n#### Impact:\n\nA malicious MCP peer may have been able to send protocol messages with non-standard field casing (e.g., \"Method\" instead of \"method\") that the SDK would silently accept. This had the potential for:\n  - **Bypassing intermediary inspection:** Proxies or policy layers that matched on exact field names may have failed to detect or filter these messages.\n  - **Cross-implementation inconsistency:** Other MCP SDKs (TypeScript, Python) use case-sensitive parsing and would reject the same messages, creating potential security-boundary confusion.\n\n####  Fix:\n\nGo's standard JSON unmarshaling was replaced with a case-sensitive decoder (github.com/segmentio/encoding) in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.\n\n#### Credits:\nMCP Go SDK thanks Francesco Lacerenza (Doyensec) for reporting this issue.","state":0,"publishedAt":"2026-02-26T22:20:08+00:00","modifiedAt":"2026-09-10T03:50:36.1395245+00:00","affected":[{"ecosystem":"Go","name":"github.com/modelcontextprotocol/go-sdk","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"1.3.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"HIGH"}],"references":["https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f","https://nvd.nist.gov/vuln/detail/CVE-2026-27896","https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0","https://github.com/modelcontextprotocol/go-sdk"],"sourceUrl":"https://github.com/advisories/GHSA-wvj2-96wp-fq3f","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-wvj2-96wp-fq3f","identifiers":["GHSA-wvj2-96wp-fq3f","CVE-2026-27896","GO-2026-4569"]},"retained":false,"historicalAffected":[]},{"revision":"c810c616b1874b25a290f6bf0bc425a0","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GO-2026-4569","aliases":["CVE-2026-27896","GHSA-wvj2-96wp-fq3f"],"title":"MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity in github.com/modelcontextprotocol/go-sdk","description":"MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity in github.com/modelcontextprotocol/go-sdk","state":0,"publishedAt":"2026-03-10T18:28:01+00:00","modifiedAt":"2026-03-23T04:52:45.041522+00:00","affected":[{"ecosystem":"Go","name":"github.com/modelcontextprotocol/go-sdk","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"1.3.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[],"references":["https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f","https://nvd.nist.gov/vuln/detail/CVE-2026-27896","https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"],"sourceUrl":"https://osv.dev/vulnerability/GO-2026-4569","license":"OSV · upstream source license applies","key":"osv:GO-2026-4569","identifiers":["GO-2026-4569","CVE-2026-27896","GHSA-wvj2-96wp-fq3f"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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