semvver

GHSA-9mgr-73fh-p55h

Malicious code in semvver (PyPI)

Details

**Severity:** Critical

**Affected versions:** `= 1.0.0`

## 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.

---

Credit: [OpenSSF](https://github.com/ossf/malicious-packages) ([source](https://github.com/ossf/malicious-packages/blob/e29c7e37b0612ba04bf703b601e4f2a2ac4a98de/osv/malicious/pypi/semvver/MAL-2026-18104.json))

**References:**
- https://github.com/ossf/malicious-packages/blob/e29c7e37b0612ba04bf703b601e4f2a2ac4a98de/osv/malicious/pypi/semvver/MAL-2026-18104.json
- https://pypi.org/project/semvver/1.0.0
- https://bad-packages.kam193.eu/pypi/package/semvver
- https://github.com/ossf/malicious-packages/blob/5b75048f63715357959b2e2456ba15740497bba3/osv/malicious/pypi/semvver/MAL-2026-18104.json
- https://www.virustotal.com/gui/file/e6d96b5500b232bea67f6f9046cfbc22d29a515c42d2af9523a15ebe8a7c4ab7
- https://github.com/ossf/malicious-packages/blob/65a30c2bd1748889a5fb95a96da4a49b781c4b60/osv/malicious/pypi/semvver/MAL-2026-18104.json
- https://github.com/advisories/GHSA-9mgr-73fh-p55h

Compromised versions (1)

= 1.0.0

Any computer that installed or ran a compromised version should be considered fully compromised. Rotate every secret on that machine from a clean environment.