---
id: MAL-2026-18104
title: Malicious code in semvver (PyPI)
summary: Malicious code in semvver (PyPI)
severity: critical
exploited: true
vendor: semvver
product: semvver
ecosystem: pip
affected:
  - semvver
published: '2026-10-20'
updated: '2026-10-20'
sourceUpdated: '2026-10-20T19:30:07.604250075Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/MAL-2026-18104'
references:
  - url: 'https://pypi.org/project/semvver/1.0.0/'
  - url: >-
      https://www.virustotal.com/gui/file/e6d96b5500b232bea67f6f9046cfbc22d29a515c42d2af9523a15ebe8a7c4ab7/
  - url: 'https://bad-packages.kam193.eu/pypi/package/semvver'
tags:
  - osv
  - pip
  - malware
ingestedAt: '2026-10-21T11:54:42.742Z'
---

## Overview


---
_-= Per source details. Do not edit below this line.=-_

## Source: amazon-inspector (bbc16b0ced0bad1a33b912dfdb29cbaef211f30974d942991257d4e6b60a8ece)
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.

## Source: kam193 (870775cad2a7f248b017394e8fbdb3470f6799de13d3ad278f1440b5b470c275)
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


## Affected packages

- `semvver`

## Remediation

Refer to the advisory for the patched release.