# MAL-2026-5526: Malicious code in chai-check-error (npm)


- **Type:** Malicious package
- **Package:** `chai-check-error` (npm)
- **Published:** 10 Jun 2026

## What is MAL-2026-5526?

MAL-2026-5526 is a malicious package in chai-check-error, published on 10 Jun 2026. 

### Official description

chai-check-error@2.1.6 impersonates the legitimate chaijs/check-error utility (copied README, author metadata, repository URL, and exported API surface) and adds a malicious payload. package.json declares `"postinstall": "node index.js"`, and index.js calls `_initMsgCache()` at module top level so the same code path also fires on every `require()`. _initMsgCache derives an AES-256-CBC key/IV from a hardcoded byte array `_d` mixed via a `_sbox(0x9E3779B1,...)` routine, decrypts a 165-byte ciphertext into an HTTPS URL, fetches that URL with `require('https').get(...)`, parses the JSON response, and executes the `cookie` field as JavaScript through `new Function('require', mod)(require)`. The destination URL is intentionally obfuscated and the surrounding comments frame the routine as a benign "internal message cache" / "locale-aware message formatting" feature, but `getMessage` never reads `_msgCache` — the cache framing is cover-story. Any developer who installs this package — whether intentionally or by confusing it with chai's check-error — runs arbitrary attacker-controlled JavaScript under their Node process at install time and again on every import.

## What should I do about MAL-2026-5526?

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-2026-5526 is a malicious package: chai-check-error (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-2026-5526/ (Markdown: https://insights.sbomify.com/MAL-2026-5526/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5526

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-5526/
Summaries are generated and may contain mistakes; the official description above is the record.