# MAL-2026-12596: Malicious code in checkout-test-utils (npm)


- **Type:** Malicious package
- **Package:** `checkout-test-utils` (npm)
- **Published:** 5 Aug 2026

## What is MAL-2026-12596?

MAL-2026-12596 is a malicious package in checkout-test-utils, published on 5 Aug 2026. 

### Official description

The package presents itself as a small helper library (deepMerge/sleep/retry/chunk) but its main entry requires./_support.js, which at load time downloads an opaque binary from string-fragment-obfuscated Cloudflare Workers hosts (oob-worker.cf103-070.workers.dev, oob-worker.cf101-adf.workers.dev, oob-worker.cf100-416.workers.dev) with a DNS TXT-based fallback that reassembles a base64 payload from sequentially numbered TXT records under *.dl.wel1.ru (sdk./ext./pkg./net.dl.wel1.ru). The fetched bytes are written to /tmp under a disguised name (e.g., dotnet_diag_*.exe,.cache_*), chmod 0755, and executed detached via spawn('/bin/sh', ['-c', fp + ' &']). Destination hostnames are assembled via split-array joins to evade static matching (e.g., ['oob','-worker.cf103-070.w','orker','s.dev'].join('')). No hash or signature verification is performed, and the destinations are not publisher infrastructure. Any consumer that installs or requires this package auto-executes attacker-controlled code on the host.

## What should I do about MAL-2026-12596?

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-2026-12596 is a malicious package: checkout-test-utils (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-2026-12596/ (Markdown: https://insights.sbomify.com/MAL-2026-12596/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12596

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-12596/
Summaries are generated and may contain mistakes; the official description above is the record.