MAL-2026-18103Critical▾ Abyssal⚠ Exploited in the wildMalicious code in semverr (PyPI)
▾ Abyssal zone — Critical with a public exploit or in-the-wild use
impact 52.3 · likelihood 0 · exploitation 18
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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.
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
semverrRefer to the advisory for the patched release.