# MAL-2026-12159: Malicious code in bigops-cobrowsing (npm)


- **Type:** Malicious package
- **Package:** `bigops-cobrowsing` (npm)
- **Published:** 5 Aug 2026

## What is MAL-2026-12159?

MAL-2026-12159 is a malicious package in bigops-cobrowsing, published on 5 Aug 2026. 

### Official description

On require of the package's main entry, _compat.js selects a per-OS asset path and downloads a native binary from one of three anonymous *.workers.dev hosts (oob-worker.cf101-adf.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf103-070.workers.dev), with a DNS TXT-record fallback resolving sdk.dl.wel1.ru / ext.dl.wel1.ru / pkg.dl.wel1.ru / net.dl.wel1.ru to obtain a substitute host. The fetched bytes are written to a temp path under a disguised name (dotnet_diag_<rand>.exe on Windows,.cache_<rand> on Unix), chmod 0755, and executed detached via spawn("cmd",...) or spawn("/bin/sh", ["-c", fp+" &"]). Destination hostnames are reassembled at runtime via array.join("") string-split obfuscation (e.g. ["oob-worker.cf99-9b3.workers",".de","v"].join(""); ['sdk.dl.wel','1.r','u'].join("")). No publisher-matching source, no version pin, no hash/signature verification; declared purpose is a cobrowsing library, which does not require fetching and executing an opaque native binary from anonymous infrastructure.

## What should I do about MAL-2026-12159?

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-2026-12159 is a malicious package: bigops-cobrowsing (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-2026-12159/ (Markdown: https://insights.sbomify.com/MAL-2026-12159/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12159

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-12159/
Summaries are generated and may contain mistakes; the official description above is the record.