CVE-2023-27991 Explained : Impact and Mitigation

This CVE refers to a post-authentication command injection vulnerability found in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35. This vulnerability could enable an authenticated attacker to execute certain OS commands remotely.

Understanding CVE-2023-27991

This section will delve deeper into what CVE-2023-27991 entails, its impact, technical details, and mitigation strategies.

What is CVE-2023-27991?

CVE-2023-27991 is a post-authentication command injection vulnerability affecting various Zyxel firmware versions. It allows authenticated attackers to remotely execute OS commands, posing a significant security risk to affected systems.

The Impact of CVE-2023-27991

The impact of this vulnerability is classified as high, with a CVSS base score of 8.8. It can lead to severe consequences such as unauthorized remote command execution, compromising the confidentiality, integrity, and availability of the affected systems.

Technical Details of CVE-2023-27991

In this section, we will explore the specifics of the vulnerability, including its description, affected systems, and the exploitation mechanism.

Vulnerability Description

The vulnerability stems from improper neutralization of special elements used in an OS command, leading to command injection. Attackers with authenticated access can leverage this flaw to execute malicious commands on the targeted systems.

Affected Systems and Versions

The following Zyxel firmware products are affected by CVE-2023-27991:

ATP series firmware versions 4.32 through 5.35
USG FLEX series firmware versions 4.50 through 5.35
USG FLEX 50(W) firmware versions 4.16 through 5.35
USG20(W)-VPN firmware versions 4.16 through 5.35
VPN series firmware versions 4.30 through 5.35

Exploitation Mechanism

To exploit this vulnerability, an authenticated attacker can inject malicious commands into the CLI command of the affected firmware versions, enabling them to execute unauthorized actions remotely.

Mitigation and Prevention

Mitigating CVE-2023-27991 requires immediate actions and long-term security practices to fortify the affected systems against potential exploits.

Immediate Steps to Take

Organizations should apply patches released by Zyxel to address the vulnerability promptly.
Monitor network traffic for any suspicious activities that could indicate exploitation attempts.
Limit access to vulnerable devices and restrict privileges to minimize the risk of unauthorized command execution.

Long-Term Security Practices

Regularly update firmware and software to ensure security patches are in place.
Conduct security assessments and penetration testing to identify and address vulnerabilities proactively.
Educate users and administrators on best practices for secure system administration and access control.

Patching and Updates

Zyxel has provided firmware updates to remediate the post-authentication command injection vulnerability in the affected products. It is crucial for users to apply these patches as soon as possible to mitigate the risks associated with CVE-2023-27991.