CVE-2023-35139 : Exploit Details and Defense Strategies

A cross-site scripting (XSS) vulnerability affecting multiple Zyxel firmware versions has been identified, potentially allowing an attacker to execute malicious scripts. Here's an overview of CVE-2023-35139 and how it impacts affected systems.

Understanding CVE-2023-35139

This section covers the vulnerability's description, impact, affected systems, and exploitation mechanism.

What is CVE-2023-35139?

CVE-2023-35139 is a cross-site scripting (XSS) vulnerability found in the CGI program of Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, and VPN series firmware versions 5.00 through 5.37. This security flaw could enable an unauthenticated LAN-based attacker to inject and execute malicious scripts on vulnerable devices.

The Impact of CVE-2023-35139

Successful exploitation of this vulnerability could lead to the execution of stored malicious scripts, allowing the attacker to steal cookies when a user accesses the specific CGI used for dumping ZTP logs.

Technical Details of CVE-2023-35139

Let's delve into the vulnerability's specifics to understand how it affects systems and what steps can be taken to mitigate and prevent potential attacks.

Vulnerability Description

The XSS flaw in the affected Zyxel firmware versions permits an unauthenticated LAN-based attacker to store and execute malicious scripts, posing a risk of cookie theft during interactions with the vulnerable CGI.

Affected Systems and Versions

Zyxel ATP series firmware versions 5.10 through 5.37, USG FLEX series firmware versions 5.00 through 5.37, USG FLEX 50(W) series firmware versions 5.10 through 5.37, USG20(W)-VPN series firmware versions 5.10 through 5.37, and VPN series firmware versions 5.00 through 5.37 are impacted by CVE-2023-35139.

Exploitation Mechanism

An unauthenticated LAN-based attacker can exploit this vulnerability by injecting and executing malicious scripts through the CGI program, potentially leading to the unauthorized retrieval of sensitive cookies.

Mitigation and Prevention

To safeguard affected systems from CVE-2023-35139, immediate and long-term security measures should be implemented, including patching and applying updates.

Immediate Steps to Take

Immediate actions to mitigate the risk posed by this vulnerability involve applying relevant security patches and updates provided by Zyxel to address the XSS issue.

Long-Term Security Practices

In the long term, it is essential to follow secure coding practices, conduct regular security assessments, and stay informed about potential security advisories and updates to prevent similar vulnerabilities.

Patching and Updates

Regularly check for and apply firmware updates released by Zyxel to ensure that the XSS vulnerability in the affected firmware versions is remedied.