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CIS 290 LINUX Security

Implement essential Linux user security measures to fortify your network. Secure passwords, configure PAM, prevent IP spoofing, kernel isolation, and service restrictions.

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CIS 290 LINUX Security

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  1. CIS 290LINUX Security User security Network Security

  2. User Security • ALWAYS use /etc/shadow (pwconv command) • Password aging: get: chage -l userid set: chage -M 60 -m 7 -W 7 userid • Lock/unlock and account passwd –l userid passwd –u userid • Limit password reuse: vi /etc/pam.d/system-auth (RHEL/Fedora) vi /etc/pam.d/common-password (Ubuntu) Add: password sufficient pam_unix.so use_authtok md5 shadow remember=10 • Verify root ID’s: awk -F: '($3 == "0") {print}' /etc/passwd • Verify no password ID’s: awk -F: '($2 == "") {print $1 }' /etc/shadow | grep /etc/passwd Make sure they are /bin/nologin • No ROOT LOGIN, use su or sudo. • Disable ROOT login under FTP., SSH, GUI (procedures vary) • Configure pam_cracklib.so to enforce the password policy. • See defaults in /etc/login.defs for /etc/shadow values.

  3. sysctl.conf For network: # Enable IP spoofing protection • net.ipv4.conf.all.rp_filter=1 # Disable IP source routing • net.ipv4.conf.all.accept_source_route=0 # Ignoring broadcasts request • net.ipv4.icmp_echo_ignore_broadcasts=1 net.ipv4.icmp_ignore_bogus_error_messages=1 • # Make sure spoofed packets get logged net.ipv4.conf.all.log_martians = 1 • # disable IPv6 net.ipv6.conf.all.disable_ipv6=1 Kernel isolation (test carefully on test system): • Turn on execshield kernel.exec-shield=1 kernel.randomize_va_space=1

  4. Network services • Determine open services: netstat –tulpn -OR- nmap -sT -O localhost • Disable with chkconfig. And/or remove software. • Use TCP_WRAPPERS (xinetd) • Configure iptables • Remove Xwindows: yum groupremove "X Window System“ • Set initdefault to runlevel 3 • No cleartext services HTTP, TELNET, FTP, rcmd, (see gov’t requirements) - use SSH, SSL, SFTP. Restrict NFS/CIFS to local networks only.

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