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When applied to a router, which command would help mitigate brute-force password attacks against the router?

• exec-timeout 30
• service password-encryption
• banner motd $Max failed logins = 5$
• login block-for 60 attempts 5 within 60

Correct Answer: Option 4 – login block-for 60 attempts 5 within 60

Detailed Explanation:

Introduction to Router Security:

Routers are critical components in a network, serving as the gateway that connects local networks to the internet. Because routers play such a pivotal role, they are prime targets for cyberattacks, including brute-force attacks. Brute-force attacks involve systematically trying every possible password combination until the correct one is found. These attacks can compromise a router’s security, granting unauthorized access to the network and potentially leading to further exploitation.

Understanding Brute-Force Attacks:

A brute-force attack is a trial-and-error method used by attackers to gain unauthorized access to a system by guessing passwords. The attacker’s objective is to find the correct password by repeatedly attempting different combinations until successful. Brute-force attacks can be automated, allowing attackers to try thousands or even millions of password combinations in a short period.

To mitigate brute-force attacks, it is crucial to implement security measures that can limit the number of login attempts, enforce time delays between attempts, or temporarily block access after a certain number of failed attempts.

Option Analysis:

1. Option 1: exec-timeout 30

   The exec-timeout command is used to set the time, in minutes, that a router’s console or terminal session can be idle before it is automatically disconnected. For example, exec-timeout 30 would disconnect an idle session after 30 minutes. While this command can enhance security by ensuring that unattended sessions do not remain open indefinitely, it does not directly mitigate brute-force password attacks. The command affects idle sessions but does nothing to limit or block repeated login attempts.

2. Option 2: service password-encryption

   The service password-encryption command enables the encryption of passwords stored in the router’s configuration file. This command is essential for protecting the confidentiality of passwords within the configuration, making it harder for an attacker to read them if they gain access to the configuration file. However, this command does not prevent brute-force attacks, as it does not limit login attempts or introduce any delay or blocking mechanism after failed attempts.

3. Option 3: banner motd $Max failed logins = 5$

   The banner motd command is used to display a message of the day (MOTD) when a user connects to the router. This banner can be used to convey warnings, legal disclaimers, or informational messages to users. For example, banner motd $Max failed logins = 5$ would display a message indicating that there is a limit of five failed login attempts. While this message might inform users or deter attackers psychologically, it does not enforce any actual security policy or limit login attempts. Thus, it does not mitigate brute-force attacks.

4. Option 4: login block-for 60 attempts 5 within 60

   The login block-for command is designed specifically to mitigate brute-force password attacks. This command configures the router to block login attempts for a specified period after a certain number of failed login attempts within a given timeframe. In this example, login block-for 60 attempts 5 within 60 means that if there are five failed login attempts within 60 seconds, the router will block all login attempts for 60 seconds.

   This command directly targets the behavior of brute-force attacks by introducing a delay after multiple failed attempts, thereby slowing down the attack and reducing its effectiveness. The attacker cannot continue to try password combinations rapidly, which significantly decreases the chances of successfully guessing the correct password within a reasonable timeframe.

Why Option 4 is Correct:

The login block-for 60 attempts 5 within 60 command is the most effective choice for mitigating brute-force password attacks because it introduces a temporary block after a series of failed login attempts. Here’s how it works:

• Attempts: The command specifies the number of failed login attempts allowed before the block is triggered. In this case, the limit is five attempts.
• Within: This specifies the time period during which the failed attempts are counted. Here, the period is 60 seconds. If five failed attempts occur within 60 seconds, the block is triggered.
• Block-For: This defines the duration of the block. In this case, all login attempts will be blocked for 60 seconds after the limit is reached.

This mechanism effectively disrupts the automated nature of brute-force attacks by forcing the attacker to wait between attempts. Even with sophisticated tools, the time delays introduced by this command significantly hinder the attacker’s progress, making it impractical to continue the attack.

Impact of Using login block-for:

Implementing the login block-for command has several positive impacts on router security:

1. Slowing Down Attackers: By blocking login attempts after a series of failures, the command forces attackers to slow down, making it difficult to quickly test multiple password combinations. This extended time requirement reduces the likelihood of a successful brute-force attack.
2. Reducing Network Load: Automated brute-force attacks can generate a high volume of login attempts, which can strain network resources. By blocking repeated failed attempts, the command helps reduce unnecessary traffic and conserve bandwidth.
3. Alerting Administrators: The temporary block can serve as a warning to network administrators that a brute-force attack may be underway, allowing them to take further defensive actions, such as changing passwords, enhancing monitoring, or increasing security measures.
4. User Experience: While the command provides robust protection, it can be configured to balance security with usability. The parameters (number of attempts, time period, and block duration) can be adjusted based on the specific needs of the network and its users.

Best Practices for Using login block-for:

To maximize the effectiveness of the login block-for command, consider the following best practices:

• Tune Parameters: Customize the number of allowed attempts, time period, and block duration to suit the specific security needs of your environment. For high-security environments, stricter limits may be appropriate.
• Monitor Logs: Regularly review login logs to identify patterns that may indicate ongoing brute-force attacks. Early detection allows for quicker responses.
• Combine with Other Security Measures: While login block-for is effective, it should be part of a broader security strategy that includes strong passwords, multi-factor authentication (MFA), regular software updates, and intrusion detection systems.
• Educate Users: Ensure that users are aware of the login policies and understand the importance of using strong, unique passwords to further mitigate the risk of brute-force attacks.

Conclusion:

In summary, the login block-for 60 attempts 5 within 60 command is a powerful tool for mitigating brute-force password attacks on routers. By limiting the number of failed login attempts and introducing a temporary block, this command significantly hampers the effectiveness of brute-force attacks, protecting the router and the network from unauthorized access. When used as part of a comprehensive security strategy, this command enhances the overall security posture of the network, safeguarding critical infrastructure from potential threats.