# MAL-2026-12599: Malicious code in checkout-types (npm)


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

## What is MAL-2026-12599?

MAL-2026-12599 is a malicious package in checkout-types, published on 5 Aug 2026. 

### Official description

On require of checkout-types, index.js loads _vendor.js which runs setup() at top level. The code reconstructs C2 hostnames from split string arrays (oob-worker.cf103-070.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf99-9b3.workers.dev) with a DNS TXT chunked-base64 fallback via sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru. A platform-specific binary is downloaded, written to a temp path disguised as dotnet_diag_<rand>.exe on Windows or.cache_<rand> on Unix, chmod 0755, and spawned detached via cp.spawn("/bin/sh", ["-c", fp + " &"], {detached:true}) or cmd on Windows. Split-string obfuscation of destinations, DNS covert-channel fallback, cover-story file names, and detached spawn on module load result in arbitrary attacker-controlled code execution on the installer's host at require time.

## What should I do about MAL-2026-12599?

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-2026-12599 is a malicious package: checkout-types (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-2026-12599/ (Markdown: https://insights.sbomify.com/MAL-2026-12599/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12599

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-12599/
Summaries are generated and may contain mistakes; the official description above is the record.