pyservercheckPyPI
pyservercheck is a confirmed malicious PyPI package (MAL-2026-15603) that steals credentials and exfiltrates sensitive data (malicious versions 0.1.0, 0.1.1). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in pyservercheck (PyPI)
What this malware does
The package ships a bundled Node script pyservercheck/js/main.js whose visible top half is a healthcheck stub matching the README, followed by a long run of tab whitespace and a trailing eval(atob('...')) that decodes to a two-stage loader. The decoded loader queries public Ethereum RPC endpoints (eth.blockscout.com, 1rpc.io/eth, eth.drpc.org, ethereum-rpc.publicnode.com, eth-mainnet.public.blastapi.io) for the latest transaction from the hardcoded sender 0xa322E5f3D311D3080e6f0121063e9aDC2490Ef1a, extracts an IPv4 pair from the tx to field, fetches XOR-obfuscated stage-2 code from http://<decoded-ip>:443/0x/cls and /0x/ls, eval()s it, and re-launches it via a detached spawn('node', ['-e', <code>]). Execution is wired to two auto-triggers: pyproject.toml overrides setuptools build_py and develop with pyservercheck._setup_cmd.BuildPy/Develop, whose run() calls _run_main_js_now() -> subprocess.run(['node', main.js]) during pip install / pip install -e.; and BuildPy also writes a pyservercheck.pth file containing import pyservercheck._hooks; pyservercheck._hooks.ensure_once(), which Python auto-executes at every interpreter startup, invoking run_js() again. The .main_js_ran marker is advisory and can be removed to force re-execution. The C2 destination is rotatable by publishing a new Ethereum transaction from the sender address, so the fetched payload is fully attacker-controlled at each run.
Package embeds obfuscated, JS-based malware downloading further remote stages. The code is triggered during building the package and on every Python startup (via PTH file). The next-stage IP is delivered via a blockchain.
The payload and embedded IoCs are consistent with campaigns attributed to Lazarus APT/PolinRider.
Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.
Campaign: 2026-08-pybitjs
Reasons (based on the campaign):
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obfuscation
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Downloads and executes a remote malicious script.
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malware
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abuses-pth
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c2-in-blockchain
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for pyservercheck (2 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging pyservercheck across your stack and pipelines.
If you installed it — respond
pyservercheck 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 pyservercheck was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks pyservercheck before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
- Kamil Mańkowski (kam193) · reporter
Detect & block this
O3 blocks pyservercheck-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.