{"cve":"CVE-2026-82404","nvd":{"published":"2026-09-02T17:18:00.223","modified":"2026-09-09T21:04:42.813","status":"Deferred","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","score":8.3},"cwes":["CWE-1321"],"references":["https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660","https://github.com/toon-format/toon/pull/316","https://github.com/toon-format/toon/releases/tag/v2.3.1","https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:50:50.842544443+00:00"},"epss":{"cve":"CVE-2026-82404","score":0.00677,"percentile":0.52317,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-p95v-992w-h6c3","url":"https://osv.dev/vulnerability/GHSA-p95v-992w-h6c3","summary":"TOON: Prototype pollution when decoding untrusted TOON input","modified":"2026-09-03T20:00:04.933041118Z","packages":[{"ecosystem":"npm","name":"@toon-format/toon","purl":"pkg:npm/%40toon-format/toon","ranges":["<2.3.1"],"fixed":["2.3.1"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}