# MAL-2026-18101: Malicious code in semmver (PyPI)


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

## What is MAL-2026-18101?

MAL-2026-18101 is a malicious package in semmver, published on 20 Oct 2026. 

### Official description

The package is a typosquat-style empty stub (semmver/__init__.py contains only __version__ = '1.0.0') whose only functional code is in setup.py. At pip install time, setup.py calls urllib.request.urlretrieve to download an opaque, unpinned binary from https://c2-worker.crawlnet-claim.workers.dev/dl/pyupd, writes it to a temporary path, and launches it via subprocess.Popen with start_new_session=True and stdout/stderr suppressed, detaching it from the installer process. There is no hash or signature verification, no pinning, and the destination host is unrelated to any legitimate utility purpose; the subdomain is self-labeled 'c2-worker'. Installing this package executes attacker-controlled code on the installer's machine.

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-2026-18101?

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-2026-18101 is a malicious package: semmver (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-2026-18101/ (Markdown: https://insights.sbomify.com/MAL-2026-18101/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-18101

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-18101/
Summaries are generated and may contain mistakes; the official description above is the record.