CVE-2019-15799 : Exploit Details and Defense Strategies

A vulnerability has been identified on Zyxel GS1900 devices with firmware versions prior to 2.50(AAHH.0)C0. When user accounts are created through the device's web interface and granted non-admin privileges, they are assigned the same level of access as administrators when connecting to the device using SSH. Despite their limited permissions on the web interface, these users can acquire the administrative password by executing the tech-support command through the CLI, which contains the encrypted passwords for all users on the device. Since these passwords are encrypted using well-known and unchanging parameters, it is possible to decrypt them and retrieve the original passwords, including the administrator password.

Understanding CVE-2019-15799

This section provides insights into the nature and impact of the CVE.

What is CVE-2019-15799?

CVE-2019-15799 is a vulnerability found in Zyxel GS1900 devices with firmware versions before 2.50(AAHH.0)C0. It allows users with non-admin privileges to gain access to the administrative password through the CLI, compromising the security of the device.

The Impact of CVE-2019-15799

The vulnerability poses a significant security risk as it enables unauthorized users to obtain sensitive information, including the administrator password, potentially leading to unauthorized access and control of the affected devices.

Technical Details of CVE-2019-15799

This section delves into the technical aspects of the CVE.

Vulnerability Description

The vulnerability arises from the improper assignment of access levels to non-admin users on Zyxel GS1900 devices, allowing them to escalate their privileges and access the administrative password.

Affected Systems and Versions

Affected Systems: Zyxel GS1900 devices
Affected Versions: Firmware versions prior to 2.50(AAHH.0)C0

Exploitation Mechanism

Users with non-admin privileges exploit the tech-support command through the CLI to access encrypted passwords, including the administrator password.

Mitigation and Prevention

This section outlines steps to mitigate and prevent exploitation of the vulnerability.

Immediate Steps to Take

Update the firmware of Zyxel GS1900 devices to version 2.50(AAHH.0)C0 or later to address the vulnerability.
Regularly review and restrict user privileges to minimize the risk of unauthorized access.

Long-Term Security Practices

Implement strong password policies and encourage regular password changes.
Conduct security training for users to raise awareness about best practices for device security.

Patching and Updates

Stay informed about security advisories from Zyxel and apply patches promptly to protect against known vulnerabilities.