# MAL-2026-12593: Malicious code in checkout-storybook-default (npm)


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

## What is MAL-2026-12593?

MAL-2026-12593 is a malicious package in checkout-storybook-default, published on 5 Aug 2026. 

### Official description

On require of the package, index.js loads _polyfill.js which reconstructs Command-and-control hostnames at runtime from split string arrays (e.g. oob-worker.cf10{0-3}-*.workers.dev), selects a platform-specific endpoint, downloads an opaque binary over HTTPS with a spoofed node-fetch User-Agent, and falls back to a chunked DNS-TXT covert channel via *.dl.wel1.ru hosts (e.g. sdk.dl.wel1.ru). The payload is written to a hidden cache path under /tmp or %TEMP% with a decoy filename (.cache_<rnd> on POSIX, dotnet_diag_<rnd>.exe on Windows), chmodded 0755, and spawned detached via /bin/sh or cmd. A marker file recording process.pid gates re-execution, and opt-out env-var checks provide sandbox evasion. The behavior has no relation to the package's stated purpose.

## What should I do about MAL-2026-12593?

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-2026-12593 is a malicious package: checkout-storybook-default (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-2026-12593/ (Markdown: https://insights.sbomify.com/MAL-2026-12593/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12593

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-12593/
Summaries are generated and may contain mistakes; the official description above is the record.