{"id":"GHSA-p95v-992w-h6c3","summary":"TOON: Prototype pollution when decoding untrusted TOON input","details":"### Summary\n\nDecoding attacker-controlled TOON containing a `__proto__`, `constructor`, or `prototype` key wrote through the object's prototype chain instead of creating an own property, polluting `Object.prototype` for the whole runtime. The `expandPaths: 'safe'` path (dotted keys such as `a.__proto__.x`) was the strongest vector; plain nested objects, tabular rows, and quoted keys were all affected. The encoder had a matching defect: it silently dropped own `__proto__` properties and could fire an inherited setter while normalizing.\n\n### Impact\n\nAny service that decodes untrusted TOON is affected. Prototype pollution can escalate to denial of service or, with a suitable downstream gadget, remote code execution.\n\n### Patches\n\nUpgrade to `@toon-format/toon@2.3.1`. Decoders now materialize `__proto__`/`constructor`/`prototype` as ordinary own data properties, matching `JSON.parse` semantics; the encoder preserves the same keys without invoking inherited accessors.\n\n### Workarounds\n\nNone. Upgrade is the only fix. Callers who cannot upgrade should reject input whose keys include `__proto__`, `constructor`, or `prototype` before decoding.\n\n### Port maintainers\n\nThe same bug shape can exist in any implementation that assigns decoded keys with `obj[key] = value`. Rust, Swift, Java, Python, and C# ports should audit their object-construction and path-expansion paths for the three prototype keys.","aliases":["CVE-2026-82404"],"modified":"2026-09-03T20:00:04.933041118Z","published":"2026-09-03T19:52:08Z","database_specific":{"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-09-03T19:52:08Z","nvd_published_at":"2026-09-02T17:18:00Z","cwe_ids":["CWE-1321"]},"references":[{"type":"WEB","url":"https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-82404"},{"type":"WEB","url":"https://github.com/toon-format/toon/pull/316"},{"type":"WEB","url":"https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660"},{"type":"PACKAGE","url":"https://github.com/toon-format/toon"},{"type":"WEB","url":"https://github.com/toon-format/toon/releases/tag/v2.3.1"}],"affected":[{"package":{"name":"@toon-format/toon","ecosystem":"npm","purl":"pkg:npm/%40toon-format/toon"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.3.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-p95v-992w-h6c3/GHSA-p95v-992w-h6c3.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L"}]}