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GHSA-p95v-992w-h6c3
@toon-format/toonSummary
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.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data. There is a low impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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