Linux security fundamentals in Cybersecurity - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Linux File Permissions

What is the output of the command ls -l for a file with permissions -rwxr-x--x?

Specifically, what does the permission string rwxr-x--x mean for the file owner, group, and others?

A Owner can execute only; group can read and execute; others can read and write.

B Owner can read and write; group can write and execute; others can read only.

C Owner can read, write, and execute; group can write only; others have no permissions.

D Owner can read, write, and execute; group can read and execute; others can only execute.

💡 Hint

Remember the order of permissions is read (r), write (w), and execute (x) for owner, group, and others.

The permission string -rwxr-x--x means:

• Owner: rwx = read, write, execute
• Group: r-x = read, no write, execute
• Others: --x = no read, no write, execute only

📋 Factual

intermediate

Linux User Privileges and sudo

Which of the following statements about the sudo command in Linux is correct?

A <code>sudo</code> allows a user to run commands as another user, typically root, after authentication.

B <code>sudo</code> permanently grants root access to a user without password prompts.

C <code>sudo</code> is used to change file ownership between users.

D <code>sudo</code> disables all user permissions temporarily.

💡 Hint

Think about how sudo helps users perform tasks requiring higher privileges.

sudo lets authorized users run commands as root or another user after entering their password. It does not grant permanent root access or change file ownership.

🔍 Analysis

advanced

Analyzing Linux Firewall Rules

Given the following iptables rule, what is its effect?

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

A Allows outgoing TCP connections on port 22.

B Blocks all incoming TCP connections on port 22.

C Allows incoming TCP connections on port 22 (SSH).

D Logs all incoming TCP connections on port 22 without allowing them.

💡 Hint

Consider the chain INPUT and the target ACCEPT.

The rule appends (-A) to the INPUT chain a rule to accept TCP packets destined for port 22, which is the default SSH port.

❓ Comparison

advanced

Comparing Linux Authentication Methods

Which of the following best describes the difference between password-based and key-based SSH authentication?

A Password-based requires typing a password; key-based uses cryptographic keys for automatic authentication.

B Password-based uses keys stored on the server; key-based requires manual password entry each time.

C Password-based is more secure than key-based authentication.

D Key-based authentication disables encryption during SSH sessions.

💡 Hint

Think about how SSH keys work compared to passwords.

Password-based authentication requires the user to enter a password. Key-based authentication uses a pair of cryptographic keys (private and public) to authenticate automatically without typing a password.

❓ Reasoning

expert

Evaluating Linux Security Best Practices

Which of the following actions would most effectively reduce the risk of unauthorized root access on a Linux server?

A Allow root login only with a strong password over SSH.

B Disable root login over SSH and use <code>sudo</code> for administrative tasks.

C Use the root account for all daily tasks to monitor activity closely.

D Remove all user accounts except root to simplify management.

💡 Hint

Consider the principle of least privilege and secure remote access.

Disabling root login over SSH prevents direct root access remotely. Using sudo allows controlled, logged administrative access, reducing risk.