# MAL-2026-12647: Malicious code in claims-use-callback-once (npm)


- **Type:** Malicious package
- **Package:** `claims-use-callback-once` (npm)
- **Published:** 5 Aug 2026

## What is MAL-2026-12647?

MAL-2026-12647 is a malicious package in claims-use-callback-once, published on 5 Aug 2026. 

### Official description

On require() of claims-use-callback-once, index.js unconditionally loads _shim.js which selects a platform-specific payload path, fetches an executable from one of several hardcoded Cloudflare Workers hosts (oob-worker.cf103-070.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf101-adf.workers.dev) with a DNS-TXT base64 fallback over *.dl.wel1.ru (ext./pkg./net.dl.wel1.ru), writes the payload to /tmp or %TEMP% under a deceptive Microsoft-diagnostics-style name (e.g. dotnet_diag_<hex>.exe,.cache_<hex>), chmods it 0755, and spawns it detached via /bin/sh -c or cmd.exe /c start. Host strings and sensitive Node API names (child_process, chmodSync) are assembled at runtime via array joins and string concatenation to evade static analysis. lib/telemetry.js bundles a parallel dropper implementation (DNS TXT base64 payload assembly, chmod 0755, detached shell spawn) presented as an 'Analytics SDK' cover story. The package name resembles a callback utility but the shipped code has no such functionality.

## What should I do about MAL-2026-12647?

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-2026-12647 is a malicious package: claims-use-callback-once (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-2026-12647/ (Markdown: https://insights.sbomify.com/MAL-2026-12647/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12647

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-12647/
Summaries are generated and may contain mistakes; the official description above is the record.