Agent skill
fail2ban
Protect servers from brute force attacks with Fail2Ban. Use when a user asks to block repeated failed login attempts, protect SSH, secure web servers from brute force, or ban malicious IPs automatically.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/fail2ban
Metadata
Additional technical details for this skill
- tags
-
fail2ban brute-force ssh security firewall
- author
- terminal-skills
- version
- 1.0.0
- category
- devops
SKILL.md
Fail2Ban
Overview
Fail2Ban monitors log files for failed authentication attempts and bans offending IPs using iptables/nftables. Protects SSH, Nginx, Apache, Postfix, and any service with log-based authentication.
Instructions
Step 1: Install
sudo apt install fail2ban
sudo systemctl enable fail2ban
Step 2: Configure
# /etc/fail2ban/jail.local — Custom configuration (never edit jail.conf)
[DEFAULT]
bantime = 1h
findtime = 10m
maxretry = 5
banaction = iptables-multiport
[sshd]
enabled = true
port = ssh
maxretry = 3
bantime = 24h
[nginx-http-auth]
enabled = true
port = http,https
maxretry = 5
[nginx-botsearch]
enabled = true
port = http,https
maxretry = 2
bantime = 7d
Step 3: Monitor
sudo fail2ban-client status # list active jails
sudo fail2ban-client status sshd # show banned IPs
sudo fail2ban-client set sshd unbanip 1.2.3.4 # unban
sudo fail2ban-client set sshd banip 5.6.7.8 # manual ban
Guidelines
- Always create jail.local — jail.conf gets overwritten on updates.
- Start conservative: 5 retries, 1h ban. Adjust based on logs.
- For modern alternative with community threat sharing, consider CrowdSec.
- Use
fail2ban-regexto test custom filters before deploying.
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