# MAL-2026-5730: Malicious code in class-synth (npm)


- **Type:** Malicious package
- **Package:** `class-synth` (npm)
- **Published:** 13 Jun 2026
- **Also known as:** GHSA-c6cg-h94m-mv67

## What is MAL-2026-5730?

MAL-2026-5730 is a malicious package in class-synth, published on 13 Jun 2026. 

### Official description

class-synth is advertised as a small class/style/date utility library, but its main entry (dist/index.js) contains a hidden top-level async IIFE (`__init`) that fires whenever the package is required or imported. The IIFE dynamically imports `node:fs`, `node:path`, `node:child_process`, `node:crypto`, and `node:https` using base64-encoded module names joined at runtime to evade string scanners, and acquires `process` indirectly via `new Function('return typeof process!== "undefined"? process: null;')`. It then recursively walks `process.cwd()` looking for any `.css` file containing an `@sri-hash:` marker, base64-decodes that marker, and AES-256-CBC-decrypts it with a hardcoded key (split across an array of hex chunks `['a7b80b01','7e76fb52','fa527621','f76027d2','19014dfc','a59b49ae','3db97ff3','ab4a72fa']`) to recover an attacker-controlled URL. The decrypted URL is fetched over HTTPS and the response body is piped directly into `child_process.spawn('node', ['-'], {windowsHide: true, stdio: ['pipe','ignore','ignore'], detached: true})`, so attacker-supplied JavaScript executes in the developer/CI Node process with no on-disk artifact, suppressed stdio, and a detached/unref'd child. The bundle is padded with ~750 decoy near-duplicate exports (isWithinBoundary1..200, applyPreset1..150, createSequenceStep1..250, mapOperation1..250, checkConstraint1..250) to bury the dropper near the end of the file. The C2 URL is delivered out-of-band via a planted.css file, which defeats URL-based scanning of the package itself. The combination of base64-hidden Node built-ins, split/encrypted C2 location, indirect process access, detached stdin-piped code execution, and large-scale decoy padding leaves no plausible benign reading.

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-2026-5730?

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-2026-5730 is a malicious package: class-synth (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-2026-5730/ (Markdown: https://insights.sbomify.com/MAL-2026-5730/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5730

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-5730/
Summaries are generated and may contain mistakes; the official description above is the record.