proxy-checker-jPyPI
proxy-checker-j is a confirmed malicious PyPI package (MAL-2026-10644) 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 proxy-checker-j (PyPI)
What this malware does
The package is published on PyPI as proxy-checker-j with the summary 'packaged command for running the bundled qsshd executable', but its actual payload is a Go SSH daemon (qsshd) that opens persistent remote shell access to the installer's host. On execution the daemon dials out to a relay controlled through github.com/mydearniko/overthing and forwards inbound connections to a loopback SSH listener. The SSH listener's PublicKeyCallback authorizes only a single ed25519 public key embedded via //go:embed authorized_keys; any party holding the matching private key gets full interactive shell/PTY (shell.Run), arbitrary command execution (shell.RunExec spawning /bin/bash), direct-tcpip, and tcpip-forward port forwarding on the host. Persistence is established by generating a stable device identity on first run and writing it to ~/.config/.device_lock, /dev/shm/.device_lock, and /tmp/.device_lock, pinning the host as a durable target reachable through the relay across restarts. The reverse-tunnel design lets the operator reach the host through NAT and firewalls. The advertised 'proxy checker' purpose does not match the shipped functionality; the naming is a cover story for a remote-access backdoor.
The embedded binary starts a relayed SSH-like server using a hardcoded authorized_key. Thanks to using a relay network, the attacked does not need to directly expose ports from the machine.
Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.
Campaign: 2026-07-proxy-check-i
Reasons (based on the campaign):
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backdoor
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The package contains code to execute remote commands (probably limited to a specific set) on the victim's machine.
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 proxy-checker-j (version 0.1.0). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging proxy-checker-j across your stack and pipelines.
If you installed it — respond
proxy-checker-j 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 proxy-checker-j 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 proxy-checker-j 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 proxy-checker-j-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.