[4 Fixes] Critical Sudo Bug CVE-2021-3156

As a Linux user, you may have heard about the critical sudo bug CVE-2021-3156. This bug, also known as “Baron Samedit”, was discovered in January 2021 and affects many popular Linux distributions, including Debian, Ubuntu, and Red Hat.

Exploiting this vulnerability could allow attackers to gain root privileges on the affected system, giving them complete control over your system and all of your data stored on it. So, in this article, I will provide a detailed explanation of the sudo bug, how it works, and provide steps on how you can fix it to secure your Linux system.

How to Fix the Sudo Bug CVE-2021-3156

If you’ve determined that your Linux system is vulnerable to the sudo bug CVE-2021-3156, you should take immediate steps to fix it. Here’s a step-by-step guide on how to do it:

1. Update the Sudo Package

The first thing you should do is update the sudo package on your system to the latest version that includes the fix for the Sudo Bug CVE-2021-3156. To do so, follow these steps:

1. Execute the following commands in the Terminal app:

sudo apt-get update && sudo apt-get upgrade

2. Wait for the apt packages and libraries to update.

3. Once you have updated your system, reboot it by running the following command:

sudo reboot

Note: If you’re using a different Linux distribution, the commands may vary. Check your distribution documentation for more information.

2. Verify the Sudo Version

After updating the sudo package, it’s important to verify that the new version is installed and running on your system. To do this, open the Terminal app and run the following command:

sudo -V

Make sure that the version number matches the latest version available from your distribution’s package manager. 

If the version is correct, then the update was successful, and your system is now protected against the sudo vulnerability. But if it isn’t that version, you should follow these steps to get the latest version, and apply the sudo bug patch:

1. Visit the sudo official website to download the patch file, for example, sudo-bug-fix.patch.
2. Once the patch file is downloaded, extract it to a directory.

tar -xf sudo-bug-fix.patch -C /home/user/patches

3. Change to the directory where the patch was extracted.

cd /home/user/patches

4. Run the patch command with sudo to apply the patch.

sudo patch < sudo-bug-fix.patch

5. Verify the patch is applied by running the sudo command with the -l flag.

sudo -l

6. If the patch was applied successfully, you should not see any error messages, and the output should show that you have permission to run any command with sudo.

3. Verify the Sudoers File

Next, you should verify that the sudoers file on your system is properly configured and does not contain any syntax errors or vulnerabilities. Here’s how you can do this:

1. Launch the Terminal window and run the following command to edit the sudoers file:

sudo visudo

2. This will open the sudoers file in the default text editor (which is usually Vim).

3. Verify that the file contains the correct entries for your system. Any modifications to this file should be done with great care, as incorrect modifications can lead to security issues.

4. Once you are done editing the file, save it with Ctrl + O and exit the editor with Ctrl + X.

5. Alternatively, you can run the following command to verify the syntax of the sudoers file:

sudo visudo -c

6. This command will check the sudoers file for syntax errors and report any issues it finds. If the file is clean, the command will return without any errors.

4. Disable Sudoedit

To further minimize the risk of exploitation is to disable the sudoedit command entirely. To do this, you can add a line to the sudoers file by following these steps:

1. Open the sudoers file for editing:

sudo visudo

2. Scroll to the bottom of the file and add the following line:

Cmnd_Alias SUDOEDIT = /usr/bin/sudoedit Defaults!SUDOEDIT !log_output

It creates a command alias called SUDOEDIT that includes the /usr/bin/sudoedit command and specifies that the log_output option is disabled for the SUDOEDIT command. Additionally, it uses the Defaults keyword to set the option for all users in the sudoers file.

3. Press Ctrl + O to save and Ctrl + X to exit the file.

Note: Modifying the sudoers file requires root access, so you may need to use the su command or sudo before the visudo command. After adding this line to the sudoers file, the sudoedit command will be disabled for all users on the system.

4 Important Points to Know About the Sudo Bug

The Critical Sudo Bug CVE-2021-3156 is a severe vulnerability in the Linux operating system that has been deemed critical by cybersecurity experts. Here are some essential points to help you understand the significance of this bug:

• 🐞 How the sudo bug can be exploited: The sudo bug can be exploited by attackers to gain root-level access to a Linux system. Attackers can use this vulnerability to execute malicious code with full administrative permissions, allowing them to steal sensitive data, install malware, and launch other types of attacks.
• 💻 Types of attacks facilitated by the sudo bug: The sudo bug can be used to facilitate various types of attacks, including privilege escalation attacks, malware installation, data theft, and backdoor creation.
• 💥 Potential damage caused by the sudo bug: The potential damage caused by the sudo bug can be severe. Attackers can use the bug to gain full control of a Linux system to steal sensitive data and launch other types of attacks. The damage can be extensive, and recovery can be difficult, especially if backups are not available.
• 🛡️ How different Linux distributions have addressed the sudo bug: Various Linux distributions have released security patches to address the vulnerability. However, some experts argue that these patches may not be enough to fully protect Linux users from the risks of the sudo bug. It is essential to keep your system up-to-date with the latest security patches to stay protected against the sudo bug.

5 Best Practices to Prevent Future Vulnerabilities

Preventing future vulnerabilities is crucial for protecting your Linux system from potential attacks. Here are some best practices for securing your system and reducing the risks of similar vulnerabilities.

• 🔒 Keep your system up-to-date with the latest security patches: Regularly updating your software and operating system is critical for protecting against known vulnerabilities. Ensure that you keep your system up-to-date with the latest security patches to reduce the risk of future vulnerabilities. Use the sudo apt-get update && sudo apt-get upgrade Linux command to update your system.
• 🛡️ Implement security measures: Implementing security measures like firewalls, intrusion detection systems, and encryption protocols can help prevent attacks, reduce their impacts, and protect your sensitive data in case of a breach. To enable the firewall, use the sudo ufw enable command in the Terminal app.
• 👨‍🏫 Train yourself on good security practices: Educating yourself on good security practices is essential in preventing future vulnerabilities. You’ll be able to identify suspicious emails and websites, use strong passwords, and limit access to sensitive data. You can also use tools, like lynis, to perform security audits and identify potential vulnerabilities.
• 🐧 Use a security-focused Linux distribution: Consider using a security-focused Linux distribution that is specifically designed to protect against known vulnerabilities. Some popular security-focused Linux distributions are Kali Linux, Tails, and Parrot Security. These distributions often come with built-in security features and are regularly updated with the latest security patches.
• 🚨 Have a plan for responding to security incidents: Even with the best security measures in place, incidents can still occur. Having a plan for responding to security incidents can help minimize damage and prevent future vulnerabilities. Ensure that you have a response plan in place and that your team is trained to execute it effectively.

Key Takeaways

The CVE-2021-3156 sudo bug is a critical vulnerability that can allow attackers to gain root access to a system. To reduce the risk of exploitation, check the sudo version, update sudo to the latest version, verify the sudoers file, and disable sudoedit to prevent user access to root files. Additionally, you should implement the best security measures, such as regular system updates, strong password policies, and limited use of the root account to reduce security risks.

If you’re interested in learning more about Linux, read the effective ways to use the hexdump command to analyze the file content, the help command to know about Linux tools, and the ls command to sort files on Bash environment. By keeping up with the latest updates can let you actively secure your system and protect it from vulnerabilities.

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