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

> Prototype pollution in Style Dictionary allows attackers to manipulate object prototypes, potentially leading to code execution or privilege escalation in Node.js environments.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2026
- **Updated:** 24 Jun 2026
- **Also known as:** GHSA-vj5c-m527-mpff

## What is CVE-2026-54639?

CVE-2026-54639 is a high-severity unsafe deserialization vulnerability in style-dictionary, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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__`.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-54639?

2 open source packages ship an affected version, including style-dictionary.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `style-dictionary` | npm | From 4.3.0 | 5.4.4 |
| `style-dictionary` | npm | From 4.3.0 | 5.4.4 |

## How do I fix CVE-2026-54639?

Upgrade style-dictionary to 5.4.4 or later.

## Is CVE-2026-54639 being exploited?

There is no known exploitation of CVE-2026-54639 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54639 and fix it if it is affected.

What it is: CVE-2026-54639 is a high-severity unsafe deserialization vulnerability in style-dictionary, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-54639 in the wild and no public exploit code.

Affected packages and fixed versions:
- style-dictionary (npm): affected from 4.3.0; fixed in 5.4.4
- style-dictionary (npm): affected from 4.3.0; fixed in 5.4.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54639/ (Markdown: https://insights.sbomify.com/CVE-2026-54639/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54639
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54639
- OSV: https://osv.dev/vulnerability/CVE-2026-54639

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54639/
Summaries are generated and may contain mistakes; the official description above is the record.