CVE-2026-82404: TOON Prototype Pollution When Decoding Untrusted Vulnerability
HIGHCVE-2026-82404 is a HIGH (CVSS 8.3) prototype pollution when decoding untrusted vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting TOON libraries in the npm ecosystem. The issue involves prototype pollution when decoding untrusted toon input. Remediation is available by upgrading affected packages to version 2.3.1.
CVE-2026-82404 at a Glance
Security Impact
CVSS: 8.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L).
How to Fix CVE-2026-82404
To remediate this vulnerability, upgrade all affected TOON dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install @toon-format/toon@2.3.1Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls @toon-format/toonHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-82404, inspect your project dependencies using npm:
npm ls @toon-format/toonAnalyze the terminal output to locate any version of TOON in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.3.1), your application is affected.
Note: The npm ls @toon-format/toon command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In TOON, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-82404 Affected TOON Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
@toon-format/toon
|
npm |
< 2.3.1
|
2.3.1
|
References
Frequently Asked Questions
What is CVE-2026-82404?
Which TOON versions are affected?
What version fixes CVE-2026-82404?
Is @toon-format/toon affected?
What is the CVSS score of CVE-2026-82404?
What CWE is associated with CVE-2026-82404?
How can I check npm dependencies for CVE-2026-82404?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-p95v-992w-h6c3",
"modified" : "2026-09-03T19:52:08Z",
"published" : "2026-09-03T19:52:08Z",
"aliases" : [ "CVE-2026-82404" ],
"summary" : "TOON: Prototype pollution when decoding untrusted TOON input",
"details" : "### Summary\n\nDecoding 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.\n\n### Impact\n\nAny service that decodes untrusted TOON is affected. Prototype pollution can escalate to denial of service or, with a suitable downstream gadget, remote code execution.\n\n### Patches\n\nUpgrade 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.\n\n### Workarounds\n\nNone. Upgrade is the only fix. Callers who cannot upgrade should reject input whose keys include `__proto__`, `constructor`, or `prototype` before decoding.\n\n### Port maintainers\n\nThe 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.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "@toon-format/toon"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.3.1"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-82404"
}, {
"type" : "WEB",
"url" : "https://github.com/toon-format/toon/pull/316"
}, {
"type" : "WEB",
"url" : "https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/toon-format/toon"
}, {
"type" : "WEB",
"url" : "https://github.com/toon-format/toon/releases/tag/v2.3.1"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-1321" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-09-03T19:52:08Z",
"nvd_published_at" : "2026-09-02T17:18:00Z"
}
}