CVE-2026-82404
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.
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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
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
- Puntuación base: 8.3
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.68%
- Percentil entre todas las CVEs puntuadas: 51
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1190Exploit Public-Facing Applicationinitial access95 % - Impacto principal
T1059Command and Scripting Interpreterexecution85 % - Impacto secundario
T1499.004Application or System Exploitationimpact75 %
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N indica explotación remota sin autenticación (T1190). Prototype pollution en decoder TOON permite RCE mediante gadgets o DoS por corrupción de Object.prototype en runtime Node.js.
Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
CWE
- CWE-1321
Referencias
JSON original (NVD)
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{
"id": "CVE-2026-82404",
"cveTags": [],
"metrics": {
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{
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"id": "CVE-2026-82404",
"role": "CISA Coordinator",
"options": [
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"exploitation": "none"
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{
"automatable": "yes"
},
{
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"version": "2.0.3",
"timestamp": "2026-09-02T18:58:59.419694Z"
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"integrityImpact": "LOW",
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"affected": [
{
"source": "security-advisories@github.com",
"affectedData": [
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"vendor": "toon-format",
"product": "toon",
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"published": "2026-09-02T17:18:00.223",
"references": [
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"url": "https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660",
"source": "security-advisories@github.com"
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"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."
}
],
"lastModified": "2026-09-09T21:04:42.813",
"sourceIdentifier": "security-advisories@github.com"
}