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CVE-2026-82404— TOON: Prototype pollution when decoding untrusted TOON input

Quick assessment

Affected
toon-format toon
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

TOON Token-Oriented Object Notation是TOON组织的一种以令牌为核心的对象符号表示法。 TOON Token-Oriented Object Notation 2.3.1之前版本存在输入验证错误漏洞，该漏洞源于解码带有__proto__、constructor或prototype键的攻击者控制的TOON时，会通过对象原型链写入而非创建自有属性，导致Object.prototype被污染，可能造成拒绝服务或远程代码执行。

CVSS 8.3 · High EPSS 0.40% · P33

Possible ATT&CK Techniques 1 AI

T1204 · User Execution

Affected Version Matrix 1

VendorProduct Version RangeStatus
toon-format toon < 2.3.1 affected
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I. Basic Information for CVE-2026-82404

Vulnerability Information
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Vulnerability Title
TOON: Prototype pollution when decoding untrusted TOON input
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1321
Source: CVE Program / CVE List V5
Vulnerability Title
TOON Token-Oriented Object Notation 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
TOON Token-Oriented Object Notation是TOON组织的一种以令牌为核心的对象符号表示法。 TOON Token-Oriented Object Notation 2.3.1之前版本存在输入验证错误漏洞，该漏洞源于解码带有__proto__、constructor或prototype键的攻击者控制的TOON时，会通过对象原型链写入而非创建自有属性，导致Object.prototype被污染，可能造成拒绝服务或远程代码执行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
toon-format toon < 2.3.1 -

II. Public POCs for CVE-2026-82404

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III. Intelligence Information for CVE-2026-82404

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Patches & Fixes for CVE-2026-82404 (2)

Vendor Advisories for CVE-2026-82404 (1)

Vendor Pages for CVE-2026-82404 (1)

IV. Related Vulnerabilities

Same weakness: CWE-1321

V. Comments for CVE-2026-82404

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