{"id":"CVE-2026-82404","summary":"TOON: Prototype pollution when decoding untrusted TOON input","details":"TOON is a compact, human-readable serialization of JSON data for LLM prompts. Prior to 2.3.1, decoding attacker-controlled TOON with a __proto__, constructor, or prototype key wrote through the object prototype chain instead of creating an own property, polluting Object.prototype for the runtime. In packages/toon/src/decode/expand.ts, the expandPaths: 'safe' path and insertPathSafe function made dotted keys such as a.__proto__.x the strongest vector, while plain nested objects, tabular rows, quoted keys, and streaming decode were also affected. The encoder also dropped own __proto__ properties and could invoke an inherited setter during normalization. Services that decode untrusted TOON could experience denial of service or, when a suitable downstream gadget is present, remote code execution. This issue is fixed in version 2.3.1.","aliases":["GHSA-p95v-992w-h6c3"],"modified":"2026-09-04T03:47:31.752522445Z","published":"2026-09-02T16:30:54.876Z","database_specific":{"cwe_ids":["CWE-1321"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82404.json","cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/toon-format/toon/releases/tag/v2.3.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82404.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660"},{"type":"FIX","url":"https://github.com/toon-format/toon/pull/316"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/toon-format/toon","events":[{"introduced":"0"},{"fixed":"94a2b7560b2b5ed903a4d466a3bce8b13daa2660"},{"fixed":"352a5b017d190cb01d6fc70e18fcaf06f9bbc6e5"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"2.3.1"}],"source":["AFFECTED_FIELD","REFERENCES"]}}],"versions":["v2.3.0","v2.2.0","v2.1.0","v2.0.1","v2.0.0","v1.4.0","v1.3.0","v1.2.0","v1.1.0","v1.0.0","v0.9.0","v0.8.0","v0.7.3","v0.7.2","v0.7.1","v0.7.0","v0.6.0","v0.5.1","v0.5.0","v0.4.1","v0.4.0","v0.3.1","v0.3.0","v0.2.1","v0.2.0","v0.1.1","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-82404.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"}]}