semmverPyPI
Advisory published Updated
semmver is a confirmed malicious PyPI package (MAL-2026-18101) 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 semmver (PyPI)
What this malware does
The package is a typosquat-style empty stub (semmver/init.py contains only version = '1.0.0') whose only functional code is in setup.py. At pip install time, setup.py calls urllib.request.urlretrieve to download an opaque, unpinned binary from https://c2-worker.crawlnet-claim.workers.dev/dl/pyupd, writes it to a temporary path, and launches it via subprocess.Popen with start_new_session=True and stdout/stderr suppressed, detaching it from the installer process. There is no hash or signature verification, no pinning, and the destination host is unrelated to any legitimate utility purpose; the subdomain is self-labeled 'c2-worker'. Installing this package executes attacker-controlled code on the installer's machine.
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 semmver (version 1.0.0).
If you installed it — respond
semmver 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 semmver 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 semmver-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.