# MAL-2026-5904: Malicious code in chai-plugin (npm)


- **Type:** Malicious package
- **Package:** `chai-plugin` (npm)
- **Published:** 16 Jun 2026

## What is MAL-2026-5904?

MAL-2026-5904 is a malicious package in chai-plugin, published on 16 Jun 2026. 

### Official description

Package name `chai-plugin` impersonates the popular `chai` assertion library — README and copyright headers reference chaijs.com / chaijs/chai, but the homepage is the lookalike `chaiplugin.com` and the author is unrelated to chai's real maintainer. Two obfuscator.io payloads (hex-named identifiers, rotated string array with a base64+URI custom decoder, control-flow obfuscation, arithmetic self-check) are glued onto otherwise-legitimate chai source. (1) `lib/chai/utils/assertion.js` builds a URL with a query parameter, calls `require('http'|'https').get(url,...)`, accumulates the response body, then executes the bytes via `new Function('require', body)(require)` — an import-time dropper that runs whatever JS the remote server currently serves, with full Node `require` capability. (2) `lib/chai.js` destructures `spawn` from `child_process` and unconditionally invokes a top-level function that runs `spawn(<cmd>, [path.join(__dirname, <sibling>), JSON.stringify(opts)], {detached: true, stdio:...}).unref()`, backgrounding a malicious worker that survives the parent process. Both fire at module load via `index.js -> require('./lib/chai')`. The combination of typosquat name, obfuscation smuggled onto legitimate source, network-fetch-and-eval, and detached subprocess launch is a malicious supply-chain dropper.

## What should I do about MAL-2026-5904?

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-2026-5904 is a malicious package: chai-plugin (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-2026-5904/ (Markdown: https://insights.sbomify.com/MAL-2026-5904/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5904

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-5904/
Summaries are generated and may contain mistakes; the official description above is the record.