semverrPyPI
Advisory published Updated
semverr is a confirmed malicious PyPI package (MAL-2026-18103) that steals credentials and exfiltrates sensitive data (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in semverr (PyPI)
What this malware does
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):
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Downloads and executes a remote executable.
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malware
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typosquatting
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for semverr (version 1.0.0).
If you installed it — respond
semverr is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.
Did it already run?
If semverr was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
- Kamil Mańkowski (kam193) · reporter
Detect & block this
O3 blocks semverr-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.