🚨 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. 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.
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GitHub
fix: harden encode and decode against prototype pollution (#316) · toon-format/toon@94a2b75
* fix: prevent prototype pollution during decode
* fix: preserve __proto__ during encode
* fix: ignore inherited tabular fields
* refactor: consolidate own-property helper and tighten __proto__ ...
September 2, 2026 8 1
