{"id":"CVE-2026-82404","state":"PUBLISHED","title":"TOON: Prototype pollution when decoding untrusted TOON input","description":"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.","publishedAt":"2026-09-02T16:30:54.876Z","updatedAt":"2026-09-02T18:59:07.868Z","severity":{"score":8.3,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","source":"GitHub_M"},"assigner":"GitHub_M","products":["toon-format toon"],"affected":[{"vendor":"toon-format","product":"toon","versions":[{"version":"< 2.3.1","status":"affected"}]}],"references":["https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3","https://github.com/toon-format/toon/pull/316","https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660","https://github.com/toon-format/toon/releases/tag/v2.3.1"],"weaknesses":["CWE-1321"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/82xxx/CVE-2026-82404.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-82404","state":"PUBLISHED","datePublished":"2026-09-02T16:30:54.876Z","dateUpdated":"2026-09-02T18:59:07.868Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-08-28T22:00:43.513Z"},"containers":{"cna":{"title":"TOON: Prototype pollution when decoding untrusted TOON input","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"toon-format","product":"toon","versions":[{"version":"< 2.3.1","status":"affected"}]}],"references":[{"url":"https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3","name":"https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/toon-format/toon/pull/316","name":"https://github.com/toon-format/toon/pull/316","tags":["x_refsource_MISC"]},{"url":"https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660","name":"https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660","tags":["x_refsource_MISC"]},{"url":"https://github.com/toon-format/toon/releases/tag/v2.3.1","name":"https://github.com/toon-format/toon/releases/tag/v2.3.1","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"LOW","baseScore":8.3,"baseSeverity":"HIGH","confidentialityImpact":"LOW","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"CHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-1321","lang":"en","description":"CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-09-02T16:30:54.876Z"},"source":{"advisory":"GHSA-p95v-992w-h6c3","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-02T18:58:59.419694Z","id":"CVE-2026-82404","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-02T18:59:07.868Z"}}]}}}