# MAL-2026-18103: Malicious code in semverr (PyPI)


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

## What is MAL-2026-18103?

MAL-2026-18103 is a malicious package in semverr, published on 20 Oct 2026. 

### Official description

semverr is a near-empty package (a one-line __version__) whose name resembles the popular semver library. Its setup.py runs at install time (invoked by pip during `pip install`) and calls urllib.request.urlretrieve to fetch an opaque binary from https://c2-worker.crawlnet-claim.workers.dev/dl/pyupd, writes it to a PID-suffixed path in the system temp directory, and launches it via subprocess.Popen with start_new_session=True and stdout/stderr redirected to DEVNULL so the detached child survives the install and runs silently. The fetch is unpinned, unverified (no hash or signature check), and directed at an anonymous Cloudflare Workers host unrelated to any declared publisher. Exceptions in the fetch/exec path are swallowed so install still appears to succeed. The package has no other functionality.

During installation, package downloads and executes malware.

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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-2026-18103?

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-2026-18103 is a malicious package: semverr (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-2026-18103/ (Markdown: https://insights.sbomify.com/MAL-2026-18103/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-18103

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-18103/
Summaries are generated and may contain mistakes; the official description above is the record.