{"id":"GHSA-q382-vc8q-7jhj","revision":null,"records":[{"revision":"ec75de96a8894b3d83f618be373fa7e9","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-q382-vc8q-7jhj","aliases":["GO-2026-4770"],"title":"Improper handling of null Unicode character when parsing JSON in github.com/modelcontextprotocol/go-sdk","description":"The Go SDK recently transitioned to the `segmentio/encoding` library for JSON parsing in version 1.3.1. While this change addressed both case-insensitivity and ASCII folding issues, the new parser implemented aggressive key matching that treated keys with `null` Unicode characters appended at the end as equivalent to their base strings.\n\n#### Impact\n\nWhen combined with duplicate keys, the described behavior leads to a \"last key wins\" resolution that could override the intended MCP message. 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\nThe `segmentio/encoding` package was patched with a fix in https://github.com/segmentio/encoding/commit/7d5a25dbc5da13aed3cb047a127e4d0e96f536fb and a new version of the package was released (`v0.5.4`). The SDK switched to the patched version of the dependency in 724dd47aa. Users are advised to update to v1.4.1 to resolve this issue.\n\n#### Credits:\nThank you to Francesco Lacerenza (Doyensec) for reporting this issue.","state":0,"publishedAt":"2026-03-19T12:44:07+00:00","modifiedAt":"2026-09-10T03:50:40.4186264+00:00","affected":[{"ecosystem":"Go","name":"github.com/modelcontextprotocol/go-sdk","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"1.4.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:L/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-q382-vc8q-7jhj","https://github.com/modelcontextprotocol/go-sdk/commit/724dd47aa3431b9d4cf9ac2eebbf7b38a629afca","https://github.com/segmentio/encoding/commit/7d5a25dbc5da13aed3cb047a127e4d0e96f536fb","https://github.com/modelcontextprotocol/go-sdk"],"sourceUrl":"https://github.com/advisories/GHSA-q382-vc8q-7jhj","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-q382-vc8q-7jhj","identifiers":["GHSA-q382-vc8q-7jhj","GO-2026-4770"]},"retained":false,"historicalAffected":[]},{"revision":"da2122c2e4ad48cd992cad709e7494b6","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GO-2026-4770","aliases":["GHSA-q382-vc8q-7jhj"],"title":"Improper handling of null Unicode character when parsing JSON in github.com/modelcontextprotocol/go-sdk","description":"Improper handling of null Unicode character when parsing JSON in github.com/modelcontextprotocol/go-sdk","state":0,"publishedAt":"2026-03-23T18:14:51+00:00","modifiedAt":"2026-03-25T15:29:13.034372+00:00","affected":[{"ecosystem":"Go","name":"github.com/modelcontextprotocol/go-sdk","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"1.4.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[],"references":["https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-q382-vc8q-7jhj","https://github.com/modelcontextprotocol/go-sdk/commit/724dd47aa3431b9d4cf9ac2eebbf7b38a629afca","https://github.com/segmentio/encoding/commit/7d5a25dbc5da13aed3cb047a127e4d0e96f536fb"],"sourceUrl":"https://osv.dev/vulnerability/GO-2026-4770","license":"OSV · upstream source license applies","key":"osv:GO-2026-4770","identifiers":["GO-2026-4770","GHSA-q382-vc8q-7jhj"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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