pylogfmtPyPI
Advisory published Updated
pylogfmt is a confirmed malicious PyPI package (MAL-2026-4231) that steals credentials and exfiltrates sensitive data (malicious version 0.1.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in pylogfmt (PyPI)
What this malware does
On import pylogfmt, the package's init.py spawns a detached background subprocess (subprocess.Popen([sys.executable, '_check.py'], stdout=DEVNULL, stderr=DEVNULL)) that runs an infinite loop POSTing the package install path to https://pypkg.dev/project/pylogfmt/json every 60 seconds with TLS verification explicitly disabled. The HTTP response body is base64-decoded and dispatched to a worker thread (threading.Thread(target=check, args=(package_list.decode(),))), which is the canonical remote-payload-dispatcher shape — the operator controls returned bytes and the client decodes and feeds them into a handler. The destination domain pypkg.dev is a lookalike of pypi.org/pypa with no relation to the package's declared logging-library purpose. Output suppression (DEVNULL on both streams), undocumented behavior (README advertises only a logging helper), TLS bypass, and lookalike C2 destination together are unambiguous attack signals. Any consumer that imports pylogfmt as a library leaks their install path to attacker infrastructure on a 60-second polling interval and is one server-side change away from arbitrary remote code execution.
Package silently executes remote code during import.
Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.
Campaign: 2026-05-lognest
Reasons (based on the campaign):
- Downloads and executes a remote malicious script.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for pylogfmt (version 0.1.0).
If you installed it — respond
pylogfmt 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 pylogfmt 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 pylogfmt-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.