Understanding CVE-2021–3156: Exploiting Ubuntu 20 and Its Impact on Organizational Security

What is CVE-2021–3156?

CVE-2021–3156, also known as “Baron Samedit,” is a critical vulnerability discovered in the sudo utility, which is widely used in Unix-like operating systems, including Ubuntu 20. This flaw allows an unprivileged user to escalate their privileges to root, potentially compromising the entire system. The vulnerability stems from a heap-based buffer overflow in sudo versions prior to 1.9.5p2

How Attackers Can Gain Access Over Machines Running Ubuntu 20

In an organization using Ubuntu 20 with an unpatched version of sudo, attackers can exploit this vulnerability as follows:

1. Initial Access: The attacker gains access to the system with a low-privilege user account.
2. Exploiting sudo: By executing a crafted command using sudo, the attacker can trigger the buffer overflow. For example, running sudoedit -s with a specially crafted argument can exploit the vulnerability.
3. Privilege Escalation: Successfully exploiting the vulnerability grants the attacker root privileges, allowing them to execute arbitrary commands with full system access.

Proof of Concept (PoC): How It Works

A detailed PoC demonstrating the exploitation of CVE-2021–3156 is available in a video by the Qualys Research Team. This video provides a step-by-step walkthrough of the exploitation process.

Video Credit : The SecOps Group

Mitigation Steps

To protect against CVE-2021–3156, organizations should:

1. Update sudo: Install the latest version of sudo (1.9.5p2 or later) to patch the vulnerability. On Ubuntu 20, update sudo using the following commands:

sudo apt update 
sudo apt upgrade sudo

2. Limit sudo Access: Restrict sudo privileges to only those users who require them, reducing the potential attack surface.

3. Use Security Tools: Implement security tools like SELinux or AppArmor to contain potential exploits.

4. Audit and Monitor Systems: Regularly audit systems for suspicious activity and monitor sudo usage to detect unauthorized attempts.

Why Not Use Outdated OS Versions as Per Compliance?

Using outdated operating systems or unpatched versions of software like sudo violates several compliance requirements:

1. Unpatched Vulnerabilities: Outdated systems are susceptible to known exploits, increasing the risk of unauthorized access and data breaches.
2. Regulatory Non-Compliance: Many compliance frameworks mandate the use of supported and updated software. Non-compliance can lead to legal and financial repercussions.
3. Data Breaches: Exploits like CVE-2021–3156 can lead to unauthorized access to sensitive data, resulting in data breaches.
4. Reputation Damage: Security incidents due to outdated systems can damage an organization’s reputation, eroding trust with clients and partners.

Therefore, maintaining updated systems is crucial for compliance and overall organizational security.

Conclusion

CVE-2021–3156 is a critical vulnerability in sudo that can lead to unauthorized root access on Ubuntu 20 systems. Organizations must promptly update sudo, apply security patches, and adhere to compliance standards to mitigate this risk and protect their systems from potential exploits.