CVE-2026-82404High· 8.3▾ TwilightTOON 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 …
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 45.7 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 3.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.4%
Last analysed / modified upstream
0.4% → 0.7%
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.
Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Affected packages:
@toon-format/toon < 2.3.1Patched in:
@toon-format/toon 2.3.1Connected by shared product, vendor, weakness, or advisory.
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