---
id: "MAL-2026-18104"
kind: "package"
aliases: ["MAL-2026-18104"]
title: "Malicious code in semvver (PyPI)"
severity: "critical"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "semvver", "fixed": [], "affected": "= 1.0.0", "ecosystem": "pypi"}]
ecosystems: ["pypi"]
tags: ["malicious", "package"]
not_affected_if: []
published_at: "2026-10-20T18:20:39+00:00"
first_seen_at: "2026-10-26T20:52:02+00:00"
updated_at: "2026-10-26T21:05:48+00:00"
sources: [{"source": "osv-malicious", "url": "https://osv.dev/vulnerability/MAL-2026-18104", "first_seen_at": "2026-10-26T20:52:02+00:00"}]
---

# Malicious code in semvver (PyPI)

## Affected

- pypi:semvver affected = 1.0.0 fixed ?

## Timeline

- 2026-10-26T20:52:02+00:00 osv-malicious https://osv.dev/vulnerability/MAL-2026-18104

## From the sources

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_-= 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

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_