Document Skill original
Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.
Linux Hardening
Secure Linux servers following CIS benchmarks and security best practices.
When to Use This Skill
Use this skill when:
- Hardening production servers
- Meeting compliance requirements
- Implementing security baselines
- Configuring secure SSH access
SSH Hardening
bash
# /etc/ssh/sshd_config
PermitRootLogin no
PasswordAuthentication no
PubkeyAuthentication yes
MaxAuthTries 3
ClientAliveInterval 300
ClientAliveCountMax 2
AllowUsers deploy admin
Protocol 2User Security
bash
# Password policy
sudo apt install libpam-pwquality
# /etc/security/pwquality.conf
minlen = 14
dcredit = -1
ucredit = -1
ocredit = -1
lcredit = -1
# Lock inactive accounts
useradd -D -f 30
# Audit sudo usage
echo "Defaults logfile=/var/log/sudo.log" >> /etc/sudoersFirewall Configuration
bash
# UFW setup
ufw default deny incoming
ufw default allow outgoing
ufw allow ssh
ufw allow 443/tcp
ufw enable
# Or iptables
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPTKernel Hardening
bash
# /etc/sysctl.d/99-security.conf
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.icmp_echo_ignore_broadcasts = 1
kernel.randomize_va_space = 2
fs.suid_dumpable = 0
# Apply
sysctl -pFile Permissions
bash
# Critical files
chmod 600 /etc/shadow
chmod 644 /etc/passwd
chmod 700 /root
chmod 600 /etc/ssh/sshd_config
# Find world-writable files
find / -type f -perm -0002 -ls
# Find SUID files
find / -perm -4000 -type f -lsAudit Configuration
bash
# Install auditd
apt install auditd
# /etc/audit/rules.d/audit.rules
-w /etc/passwd -p wa -k identity
-w /etc/shadow -p wa -k identity
-w /etc/sudoers -p wa -k actions
-a always,exit -F arch=b64 -S execve -k execBest Practices
- Disable unused services
- Keep system updated
- Use fail2ban for intrusion prevention
- Enable SELinux/AppArmor
- Regular security audits
- Monitor log files
- Implement least privilege
Related Skills
- cis-benchmarks - Compliance scanning
- firewall-config - Firewall rules
