CVE-2026-54639 is a high-severity (CVSS 8.8) CWE-1321 vulnerability in style-dictionary. A fix is available for style-dictionary — see the affected versions and patch details below.
Style Dictionary - Prototype Pollution in convertTokenData utility function
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-54639.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-54639 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
style-dictionarynpmDescription
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.tokensproperty with thesd.tokenMapproperty 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.tokensproperty with thesd.tokenMapproperty.
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.
Patches
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
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.')
}
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | style-dictionary | ≥ 4.3.0&&< 5.4.4 | 5.4.4npm install style-dictionary@5.4.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for style-dictionary, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update style-dictionary to 5.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54639 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-54639 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-54639. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-54639 in your dependencies?
O3 Security finds CVE-2026-54639 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.