创建无Shell、无特殊权限高密码用户的安全风险及运维方案

Great question—let’s break this down into clear sections to cover both the risk assessment and practical solutions tailored to your use case.

一、无Shell、无特殊权限+强密码用户的安全风险？ #

First off: these "bait" or "honeypot" users carry minimal inherent risk if configured correctly. But there are a few edge cases to watch for:

• Double-check that the user has zero usable access: Set their shell to /sbin/nologin or /usr/sbin/nologin (so they can’t log in via SSH or console), remove any sudo privileges, and either omit a home directory or set it to a root-owned folder with strict 700 permissions.
• Log bloat risk: A flood of brute-force attempts targeting the bait user can fill up your log partition if you don’t have proper log rotation in place. Make sure tools like logrotate are configured to archive and prune old auth logs regularly.
• Avoid accidental permission inheritance: Don’t add the bait user to any user groups (even default ones like users)—keep their profile as stripped-down as possible.

二、创建这类诱饵用户的合理性分析 #

Your reasoning is spot-on—these users are a smart defensive tactic for exactly the reasons you listed:

• Redirect attacker focus: Bad actors almost always target common usernames like admin, root, or test. Turning these into bait users wastes their time on invalid attempts, while your real user (like smr) flies under the radar.
• Simplify threat detection: Any login attempt on a bait user is guaranteed to be suspicious. This eliminates false positives from real users mistyping their passwords, making it easier to flag and investigate actual attacks.
• Centralize malicious activity logging: You can set up dedicated alerts for failed attempts on bait users, so you’re immediately notified when someone is probing your system.

三、过多可疑尝试：通知管理员与最佳应对方案 #

1. Alerting Administrators #

• Use fail2ban for automated alerts & blocking: This tool is purpose-built for this scenario. It monitors auth logs, triggers alerts when failure thresholds are hit, and can automatically ban malicious IPs.
  Example fail2ban jail configuration (add to jail.local):

  [bait-users]
  enabled = true
  filter = sshd
  logpath = /var/log/auth.log
  maxretry = 3  # Trigger alert after 3 failed attempts
  bantime = 3600  # Ban IP for 1 hour
  action = %(action_mwl)s  # Send email with log details
  

• Custom notifications for enterprise tools: If you use Slack, Teams, or internal alerting systems, write a simple shell/Python script to scan auth logs periodically. When failed attempts on bait users spike, send a message via the platform’s API.

2. Best Response Actions #

• Automate IP blocking: Let fail2ban or iptables/ufw handle temporary bans to stop brute-force attempts in real time. Just make sure you have a way to manually unban legitimate IPs if needed.
• Analyze attack patterns: Regularly review logs for bait users to spot trends—like repeated IP ranges, common password lists, or attack timing. Use this data to update your defenses (e.g., add persistent IP blocks for repeat offenders with ipset).
• Hardening real user accounts: Since bait users draw fire, double down on securing your actual users: Enable SSH key-only login (disable password auth entirely), enforce strong MFA, and limit sudo access to only necessary users.
• Monitor log disk usage: Set up alerts for your log partition (e.g., via monit or systemd timers) to notify you if usage exceeds 80%—this prevents log bloat from crashing critical system logging.

内容的提问来源于stack exchange，提问作者Levite