TOON: Prototype pollution when decoding untrusted TOON input

### Summary Decoding attacker-controlled TOON containing a `__proto__`, `constructor`, or `prototype` key wrote through the object's prototype chain instead of creating an own property, polluting `Object.prototype` for the whole runtime. The `expandPaths: 'safe'` path (dotted keys such as `a.__proto__.x`) was the strongest vector; plain nested objects, tabular rows, and quoted keys were all affected. The encoder had a matching defect: it silently dropped own `__proto__` properties and could fire an inherited setter while normalizing. ### Impact Any service that decodes untrusted TOON is affected. Prototype pollution can escalate to denial of service or, with a suitable downstream gadget, remote code execution. ### Patches Upgrade to `@toon-format/toon@2.3.1`. Decoders now materialize `__proto__`/`constructor`/`prototype` as ordinary own data properties, matching `JSON.parse` semantics; the encoder preserves the same keys without invoking inherited accessors. ### Workarounds None. Upgrade is the only fix. Callers who cannot upgrade should reject input whose keys include `__proto__`, `constructor`, or `prototype` before decoding. ### Port maintainers The same bug shape can exist in any implementation that assigns decoded keys with `obj[key] = value`. Rust, Swift, Java, Python, and C# ports should audit their object-construction and path-expansion paths for the three prototype keys. Source Code Location: https://github.com/toon-format/toon Affected Packages: - npm:@toon-format/toon, affected < 2.3.1, patched in 2.3.1 CWEs: - CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') CVSS: - Primary: score 8.3, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L - CVSS_V3: score 8.3, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L References: - https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3 - https://nvd.nist.gov/vuln/detail/CVE-2026-82404 - https://github.com/toon-format/toon/pull/316 - https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660 - https://github.com/toon-format/toon/releases/tag/v2.3.1 - https://github.com/advisories/GHSA-p95v-992w-h6c3