Google Compute Engine Ubuntu实例遭DoS攻击后的防护方案咨询

Sorry to hear your GCP Ubuntu VM got hijacked for a DoS attack—you’ve already taken some solid initial steps, but let’s dig into the critical next moves to lock things down for good and resolve that persistent alert.

1. Isolate the Compromised VM Right Now #

• Shut down the affected VM immediately if you haven’t already—this cuts off ongoing DoS traffic at the source.
• Don’t try to salvage this VM: Attackers almost always leave hidden backdoors (like modified system files, hidden cron jobs, or persistent malware) that are extremely hard to fully root out. Instead, take a disk snapshot first (for optional forensic analysis) then delete the original VM entirely.

2. Forensic Deep Dive (If You Want to Find the Entry Point) #

If you need to figure out how attackers gained access, attach the disk snapshot to a new, clean VM and run these checks:

• Scan SSH logs for suspicious activity: journalctl -u sshd | grep "Failed password" | head -20 (look for repeated brute-force attempts or logins from unknown IPs).
• Review bash histories for all users: cat /home/*/.bash_history and cat /root/.bash_history—this might show the commands attackers ran after gaining access.
• Check for malicious scheduled tasks: crontab -l (for your user), plus /etc/cron.d/, /etc/cron.hourly/, and /etc/systemd/system/ for hidden timers.
• Hunt for unusual processes: ps aux --sort=-%cpu | head -15—look for unrecognized processes hogging CPU or bandwidth.

3. Deploy a Clean VM and Harden It Properly #

Spin up a brand new Ubuntu VM in GCP, then apply these hardening rules to prevent future breaches:

• SSH Hardening (Beyond Port Changes):
  • Disable password authentication entirely—use SSH keys only. Edit /etc/ssh/sshd_config: set PasswordAuthentication no and PermitRootLogin no, then restart SSH with sudo systemctl restart sshd.
  • Restrict SSH access to your trusted IPs only via GCP Firewall Rules (never open port 22 to 0.0.0.0/0).
• Layered Firewall Protection:
  • Use GCP’s VPC Firewall to block all unnecessary inbound/outbound traffic—only allow ports your application actually needs (e.g., 80/443 for a web app, your custom SSH port from your IP).
  • Enable Ubuntu’s built-in ufw firewall as an extra safety net:

    sudo ufw enable
    sudo ufw allow from YOUR_TRUSTED_IP to any port YOUR_SSH_PORT
    sudo ufw allow 80/tcp  # Only if you need web traffic
    

• Automatic Security Updates:
  • Enable unattended upgrades to patch critical vulnerabilities automatically: sudo dpkg-reconfigure unattended-upgrades and follow the prompts.

4. Resolve the Persistent GCP DoS Alert #

Even after stopping the attack, GCP’s monitoring systems might keep sending alerts for a short while as logs process. To fix this:

• Check GCP’s Security Command Center (if enabled) for detailed attack metrics—this will show you traffic timestamps and targets to confirm the attack has stopped.
• If the alert lingers, reach out to GCP Support via the Console. Share details of the steps you’ve taken (isolating the VM, destroying it, deploying a clean system) and ask them to clear the alert once they verify malicious traffic has ceased.

5. Long-Term Protection to Stay Safe #

• Leverage GCP’s Built-in Security Tools:
  • Enable VM Threat Detection in Security Command Center—it flags unusual activity like brute-force attacks, malware execution, and outbound DoS traffic.
  • Use Identity-Aware Proxy (IAP) for SSH access instead of exposing ports publicly—this adds an extra authentication layer and removes the need to open SSH to the internet.
• Monitor for Anomalies:
  • Set up alerts in GCP Operations Suite for unexpected spikes in outbound bandwidth, failed SSH attempts, or new process launches.
  • Install fail2ban on your VM to auto-block IPs that repeatedly fail SSH logins:

    sudo apt install fail2ban
    sudo systemctl enable --now fail2ban
    

• Regular Audits:
  • Periodically review your GCP firewall rules, IAM permissions, and VM configurations to catch misconfigurations before attackers exploit them.
  • Use GCP’s Vulnerability Scanner to scan VMs for unpatched software vulnerabilities.

内容的提问来源于stack exchange，提问作者ojoma