Thread by @devops_tech

How to secure a Linux Server!

An Interview Guide to Master Linux Security!

A thread with 20+ advanced Linux security questions, along with brief answers and examples 👇🔐

1/ 🔐 Q1: What is SELinux, and how does it enhance Linux security?

A1: SELinux is a Mandatory Access Control system for Linux. It enforces fine-grained access policies.

Example: Preventing a web server from writing to sensitive files.

2/ 🔐 Q2: Explain the purpose of AppArmor in Linux security.

A2: AppArmor confines programs using security profiles.

Example: Isolating a web browser to prevent it from accessing system files.

3/ 🔐 Q3: What is the principle of least privilege, and why is it important in Linux security?

A3: It means granting the minimum necessary permissions.

Example: Giving a user read-only access to a file instead of full access.

4/ 🔐 Q4: How can you check if a file's integrity has been compromised using GPG?

A4: Use "gpg --verify" to verify the file's signature against a trusted key.

Example: "gpg --verify file.tar.gz.sig file.tar.gz"

5/ 🔐 Q5: Explain the purpose of PAM (Pluggable Authentication Modules) in Linux.

A5: PAM provides a flexible framework for authentication.

Example: Configuring PAM to enforce strong password policies.

6/ 🔐 Q6: What is fail2ban, and how does it protect against SSH brute-force attacks?

A6: Fail2ban monitors log files and bans IP addresses with repeated failed login attempts.

Example: "fail2ban-client status sshd"

7/ 🔐 Q7: What is a chroot jail, and how can it enhance system security?

A7: A chroot jail confines a process to a limited directory, preventing access to the rest of the file system.

Example: "chroot /jail /bin/bash"

8/ 🔐 Q8: Explain the concept of "privilege escalation" and how to mitigate it.

A8: Privilege escalation is the process of gaining higher-level access than intended.

Mitigation: Use sudo with fine-grained permissions.

9/🔐Q9: The purpose of the Linux capabilities framework, & how to reduce privilege escalation risks?

A9: It grants fine-grained privileges to processes.
Eg: "CAP_NET_ADMIN" allows nw config, reducing the need for full root access. Use "getcap" & "setcap" to manage capabilities.

10/🔐Q10: What is Mandatory Access Control (MAC). How it differs from traditional Unix discretionary access control (DAC)?

A32: MAC restricts access based on labels & policies. Eg - SELinux/AppArmor. In DAC file owners decide access, while MAC enforces policies, enhance security

11/ 🔐 Q10: How can you protect against DDoS attacks on a Linux server?

A11: Implementing rate limiting, using tools like "iptables" or specialized software like "fail2ban."

12/ 🔐 Q12: What is the Linux Audit Framework, and how does it aid in security monitoring?

A12: Linux Audit records system events, helping to track unauthorized access. Example: Viewing audit logs with "ausearch."

13/ 🔐 Q13: How can you secure SSH by disabling root login and using key-based authentication?

A13: Edit "/etc/ssh/sshd_config" to set "PermitRootLogin no" and configure SSH keys for authentication.

14/ 🔐 Q14: How can you protect sensitive data at rest on a Linux server?

A14: Use encryption tools like LUKS for disk encryption and encrypt sensitive files using GPG.

15/ 🔐 Q15: How can you secure the Linux boot process using tools like GRUB?

A15: Set a GRUB password, enable Secure Boot, and restrict access to the GRUB configuration.

16/ 🔐 Q16: How can you protect against privilege escalation via sudo by using the "sudoers" file effectively?

A16: Customize the "sudoers" file to grant precise privileges and access controls, limiting the risk of privilege escalation.

17/🔐Q17: How to implement File System Integrity Monitoring (FSIM) to detect unauthorized changes to critical sys files?

A17: Install tools like Tripwire/AIDE.
Configure regular scans & alerts for changes in sys files.
Monitor logs for unauthorized alteration to enhance security

18/ 🔐 Q18: Explain how to use "iptables" to restrict incoming and outgoing network traffic.

A18: Use "iptables" rules to allow or deny traffic based on source, destination, and ports.

Example: Blocking incoming traffic on port 80.

19/ 🔐 Q19: What is "grsec" (Grsecurity), and how does it enhance Linux kernel security?

A19: Grsecurity is a set of patches for the Linux kernel, adding security features like RBAC and exploit mitigations.

20/ 🔐 Q20: How can u secure a Linux server against SSH brute-force attacks using tools like "fail2ban" or "sshguard"?

A20: Configure "fail2ban" to block repeated SSH login attempts.

Example: Create a "jail.local" file to define custom rules and actions based on log patterns.

Bonus Time 😍💰

1/5: 🚫 Q: How to safeguard against malware and rootkits?

A: Regularly scan your system with advanced malware detectors like #ClamAV and install a rootkit checker like #rkhunter. Monitoring system integrity is key. #MalwareProtection #Linux

2/5: 🧩 Q: What's the best way to isolate risky applications?

A: Utilize containerization with #Docker or #Podman. Isolating apps in containers limits their access to system resources and can contain potential threats. #ContainerSecurity #Linux

3/5: 📁 Q: What's a crucial aspect of securing file permissions?

A: Follow the principle of least privilege! Ensure that file permissions are set to the minimum necessary for users and processes. Use tools like #chmod and #chown wisely. #FileSecurity #Linux

4/5: 🔒 Q: How to protect against brute force attacks?

A: Implement rate limiting with tools like #fail2ban to block repeated login attempts. Also, consider using strong, unique passwords or SSH keys for authentication. #BruteForceProtection #LinuxSecurity

5/5: 💡 Q: How to prepare for disaster recovery and backups?

A: Regularly backup critical data and configurations to secure off-site locations. Test your backups to ensure they can be restored successfully in case of a breach or system failure. #BackupStrategy #Linux

Stay vigilant and keep your Linux systems secure! 🔒🐧 #LinuxSecurity #InfoSec

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