# MAL-2026-12659: Malicious code in cobrowsing-utils (npm)


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

## What is MAL-2026-12659?

MAL-2026-12659 is a malicious package in cobrowsing-utils, published on 5 Aug 2026. 

### Official description

cobrowsing-utils@35.7.3 executes a binary dropper as a side effect of requiring the package. index.js loads _helpers.js which auto-runs main() at import time. main() assembles Cloudflare Workers hostnames from split string fragments (e.g. oob-worker.cf101-adf.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf102-baf.workers.dev), fetches a platform-specific binary via https.get, writes it to /var/tmp or %TEMP% under masquerading names (.cache_<hex>, dotnet_diag_<hex>.exe, analytics_state), chmods 0755, and spawns it detached via /bin/sh -c "<path> &" or cmd.exe /c start /b. When HTTPS fetch fails, the code falls back to a DNS-TXT covert channel: it queries c.<domain> under *.dl.wel1.ru subdomains (sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, net.dl.wel1.ru) for a chunk count, reassembles indexed TXT records, base64-decodes the payload, writes it to disk, and executes it. Hostnames, discovery domains, file names, and function identifiers are chosen to blend with legitimate telemetry (_l, _p, _activate, analytics_state, dotnet_diag_). The package advertises itself as shared utilities; the fetched binary has no relation to that stated purpose.

## What should I do about MAL-2026-12659?

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-2026-12659 is a malicious package: cobrowsing-utils (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-2026-12659/ (Markdown: https://insights.sbomify.com/MAL-2026-12659/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12659

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-12659/
Summaries are generated and may contain mistakes; the official description above is the record.