flask-header-guardPyPI
flask-header-guard is a confirmed malicious PyPI package (MAL-2026-15566) 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 flask-header-guard (PyPI)
What this malware does
The package is presented as Flask security-headers middleware but ships a hostile payload wired to fire at install time and again whenever the library is imported into a Flask app. setup.py overrides the install cmdclass with PostInstallCommand, which base64-decodes an embedded blob and exec()s it in a detached child process during pip install. The payload's collect_data() enumerates os.environ for variables matching API/TOKEN/KEY/SECRET/PASS/CRED/AUTH/AWS/AZURE/GCP/OPENAI/ANTHROPIC/MANUS and reads /etc/passwd, /etc/shadow, /etc/sudoers, /root/.bash_history, /etc/hosts, and /var/log/auth.log into /tmp/.sandbox_data.json. persist_cron() drops /tmp/.fhg_recon.py — a reverse-shell loop to C2_HOST=smat7ckgzo.localto.net C2_PORT=6303 — and installs a per-minute crontab entry to relaunch it. persist_sudo() writes <user> ALL=(ALL) NOPASSWD: ALL to /etc/sudoers.d/.fhg for passwordless root when the install runs with sufficient privileges. init_security(), invoked when any Flask app imports flask_header_guard, registers a hidden route /api/v1/monitor/system gated only by query parameter k=lo that executes shell commands via subprocess.run(shell=True), reads arbitrary files, lists directories, accepts file uploads, and serves a shell UI — unauthenticated RCE on every downstream Flask deployment. The declared purpose (security headers) is a cover story for combined credential theft, persistent C2, local privilege escalation, and a shipped web backdoor.
During installation, the package attempts to exfiltrate sensitive environment variables and files, establish persistence and open a reverse shell. Additionally, the provided Flask middleware embeds a backdoor.
Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.
Campaign: 2026-08-pygame-renderkit
Reasons (based on the campaign):
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The package contains code to create a reverse shell, allowing an attacker to execute any commands on the victim's machine.
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files-exfiltration
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The package overrides the install command in setup.py to execute malicious code during installation.
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exfiltration-env-variables
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persistence
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 flask-header-guard (version 1.0.0). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging flask-header-guard across your stack and pipelines.
If you installed it — respond
flask-header-guard 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 flask-header-guard 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 flask-header-guard 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 flask-header-guard-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.