# MAL-2026-18104: Malicious code in semvver (PyPI)


- **Type:** Malicious package
- **Package:** `semvver` (PyPI)
- **Published:** 20 Oct 2026

## What is MAL-2026-18104?

MAL-2026-18104 is a malicious package in semvver, published on 20 Oct 2026. 

### Official description

setup.py performs an install-time fetch-and-execute: it calls urllib.request.urlretrieve against https://c2-worker.crawlnet-claim.workers.dev/dl/pyupd, writes the response to a temporary path, and spawns it as a detached background process via subprocess.Popen with start_new_session=True. The fetch is unpinned and has no hash or signature verification, exceptions are swallowed, and the destination is a Cloudflare Workers subdomain unrelated to any PyPI publisher identity. The package has no other functionality — __init__.py is empty and the description is a generic 'utility helpers' string — so the install hook is the package's entire payload. The downloaded binary name 'pyupd' is a cover-story label; the behavior is a classic install-time dropper that grants whoever controls the Workers endpoint arbitrary code execution on the installer's host, running detached and persisting beyond the pip process.

During installation, package downloads and executes malware.

---

Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.

Campaign: 2026-10-semvver

Reasons (based on the campaign):

 - Downloads and executes a remote executable.

 - malware

 - typosquatting

## What should I do about MAL-2026-18104?

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-2026-18104 is a malicious package: semvver (PyPI). 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-2026-18104/ (Markdown: https://insights.sbomify.com/MAL-2026-18104/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-18104

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-18104/
Summaries are generated and may contain mistakes; the official description above is the record.