CVE-2026-54639

CVE-2026-54639 is a high-severity security vulnerability in style-dictionary (npm), affecting versions >= 4.3.0, < 5.4.4. It is fixed in 5.4.4.

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Summary

Style Dictionary - Prototype Pollution in convertTokenData utility function

Workarounds

A workaround is to sanitize your token data first. Whether using DTCG format or old Style Dictionary format, you have to check the token data object recursively for any object keys that include __proto__.

You can do this with the StyleDictionary instance too, just ensure that expand has to be set to false to prevent the second method of this vulnerability from happening.

const sd = new StyleDictionary({ expand: false });

if (sd.allTokens.some(tok => tok.key.includes('__proto__')) {
  throw new Error('Found malicious token key, attempting to do prototype pollution.')
}

Impact

Prototype pollution.
A malicious user can create a token array [{ key: '{__proto__.foo}', value: 'malicious' }], when processed by convertTokenData() utility function, it will pollute the Object.prototype globally where {}.foo will equal { key: '{__proto__.foo}', value: 'malicious' }.

This has been confirmed with a test/reproduction.

You are impacted when:

  • direct usage of convertTokenData(tokens, { output: 'object' });
  • indirect usage, via using Expand API https://styledictionary.com/reference/config/#expand. If your expand config deems it necessary to run expand (this means, if NOT: 1) set to false, 2) all subprops set to false, or 3) undefined), then we sync the sd.tokens property with the sd.tokenMap property by converting tokenData map back to object.
  • indirect usage via SD's transform lifecycle. Once your tokens are transformed, we also have to sync the sd.tokens property with the sd.tokenMap property.

Impact is high for this when style-dictionary is used as an integration in a NodeJS server application.
Impact is moderate for when style-dictionary is used as an integration in a Web application.
Impact is low for most common cases where the user of style-dictionary also maintains the tokens, and access is limited via read/write access to the repository/workflows where it is used.

CVE-2026-54639 has a CVSS score of 8.8 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.4.4); upgrading removes the vulnerable code path.

Affected versions

style-dictionary (>= 4.3.0, < 5.4.4)

Security releases

style-dictionary → 5.4.4 (npm)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

A patch has been published: version 5.4.4.
Any version within range >=4.3.0 <5.4.4 contains this vulnerability, see commit hash 209085d for when the vulnerability was added.

See PR with repro + fix https://github.com/style-dictionary/style-dictionary/pull/1702

Frequently Asked Questions

  1. What is CVE-2026-54639? CVE-2026-54639 is a high-severity security vulnerability in style-dictionary (npm), affecting versions >= 4.3.0, < 5.4.4. It is fixed in 5.4.4.
  2. How severe is CVE-2026-54639? CVE-2026-54639 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which versions of style-dictionary are affected by CVE-2026-54639? style-dictionary (npm) versions >= 4.3.0, < 5.4.4 is affected.
  4. Is there a fix for CVE-2026-54639? Yes. CVE-2026-54639 is fixed in 5.4.4. Upgrade to this version or later.
  5. Is CVE-2026-54639 exploitable, and should I be worried? Whether CVE-2026-54639 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-54639 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-54639? Upgrade style-dictionary to 5.4.4 or later.

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