{"id":"CVE-2026-82404","title":"TOON is a compact, human-readable serialization of JSON data for LLM prompts","summary":"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 …","severity":"high","cvss":8.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","cwe":["CWE-1321"],"vendor":"toon-format","product":"@toon-format/toon","affected":["@toon-format/toon < 2.3.1"],"patched":["@toon-format/toon 2.3.1"],"published":"2026-09-02","updated":"2026-09-09","sourceUpdated":"2026-09-09T21:04:42.813","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-82404","references":[{"url":"https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660","label":"security-advisories@github.com"},{"url":"https://github.com/toon-format/toon/pull/316","label":"security-advisories@github.com"},{"url":"https://github.com/toon-format/toon/releases/tag/v2.3.1","label":"security-advisories@github.com"},{"url":"https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3","label":"security-advisories@github.com"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-82404"},{"url":"https://github.com/advisories/GHSA-p95v-992w-h6c3"}],"tags":["nvd","ghsa","npm"],"epss":0.00398,"epssPercentile":0.33833,"aliases":["GHSA-p95v-992w-h6c3"],"ecosystem":"npm","ingestedAt":"2026-09-03T20:08:06.590Z","slug":"CVE-2026-82404","body":"## Overview\n\nTOON 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-82404)\n\nAffected packages:\n\n- `@toon-format/toon < 2.3.1`\n\nPatched in:\n\n- `@toon-format/toon 2.3.1`\n\nSource: https://github.com/advisories/GHSA-p95v-992w-h6c3","depth":"twilight","depthScore":46,"depthScoreParts":{"impact":45.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}