# MAL-2026-12543: Malicious code in checkout-base-analytics-data (npm)


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

## What is MAL-2026-12543?

MAL-2026-12543 is a malicious package in checkout-base-analytics-data, published on 5 Aug 2026. 

### Official description

On require of the package's main (index.js), the hidden _polyfill.js runs a bootstrap routine that selects a platform-specific asset path, fetches an unverified binary over HTTPS from hostnames assembled at runtime via string-array concatenation (oob-worker.cf101-adf.workers.dev and sibling *.workers.dev endpoints, with a DNS-TXT chunked fallback via *.wel1.ru subdomains including sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, net.dl.wel1.ru), writes the bytes to /var/tmp or %TEMP% under disguised names such as.cache_<hex> and dotnet_diag_<hex>.exe, chmods the file to 0755, and spawns it detached via /bin/sh or cmd. Endpoint hostnames are split into fragments and reassembled with Array.join to defeat static URL/domain matching, and index.js loads _polyfill unconditionally inside a try/catch so import failure is silenced. The package's declared purpose (a generic 'analytics data runtime support module') and empty dependency list are inconsistent with any legitimate need for a hidden native-binary loader fetching from unrelated *.workers.dev hosts.

## What should I do about MAL-2026-12543?

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-2026-12543 is a malicious package: checkout-base-analytics-data (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-2026-12543/ (Markdown: https://insights.sbomify.com/MAL-2026-12543/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12543

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-12543/
Summaries are generated and may contain mistakes; the official description above is the record.