Source: cret@cert.org
ZyXEL PMG5318-B20A devices with firmware 1.00AANC0b5 allow remote authenticated users to obtain administrative privileges by leveraging access to the user account.
ZyXEL PMG5318-B20A devices are vulnerable to a critical security flaw allowing remote, authenticated users to escalate their privileges to administrative access. This vulnerability grants attackers complete control over the device, enabling them to intercept network traffic, modify configurations, and potentially pivot to other systems on the network.
Step 1: Authentication: An attacker gains valid user credentials for the ZyXEL PMG5318-B20A device, likely through phishing, brute-force, or default credential exploitation.
Step 2: Privilege Escalation: The attacker, logged in as a standard user, identifies and exploits a specific function or API call within the device's web interface or command-line interface (CLI) that lacks proper authorization checks.
Step 3: Command Execution: The attacker crafts a malicious request (e.g., a specially crafted HTTP request or CLI command) that leverages the vulnerability to execute commands with administrative privileges.
Step 4: Administrative Access: The malicious request bypasses the authorization checks, and the device executes the attacker's commands with administrative privileges, granting the attacker full control over the device.
The vulnerability stems from insufficient access control checks within the device's firmware. Specifically, the firmware fails to properly validate the privileges of an authenticated user when handling certain administrative functions. This allows a user with standard user credentials to bypass authorization checks and execute commands with elevated privileges. The root cause is likely a missing or improperly implemented access control list (ACL) or a flaw in how the device handles user roles and permissions. The lack of proper input validation or sanitization further exacerbates the issue, potentially allowing for command injection or other related attacks. The vulnerability is triggered by exploiting a logic flaw in the firmware's authentication or authorization mechanisms, allowing a standard user to execute privileged commands.
Due to the nature of the vulnerability, it is likely to be exploited by various threat actors, including those seeking to establish a foothold within a network for further attacks. The vulnerability could be used by financially motivated actors, nation-state actors, or opportunistic attackers. This vulnerability could be used as part of a larger attack chain. CISA KEV status: Unknown (Due to the age and lack of specific information, it is difficult to determine if CISA has added it to the KEV list. However, given the potential impact, it is likely to be considered a high-priority vulnerability).
Monitor network traffic for suspicious HTTP requests or CLI commands targeting the device's administrative interfaces.
Analyze device logs for unusual activity, such as unauthorized configuration changes or attempts to access privileged functions.
Implement intrusion detection systems (IDS) with signatures specifically designed to detect exploitation attempts against this vulnerability.
Monitor for changes in the device's configuration, such as the addition of new users or modifications to existing user accounts.
Review device firmware for any unauthorized modifications or backdoors.
Upgrade the device's firmware to a patched version that addresses the vulnerability. (Check the vendor's website for available updates.)
Implement strong password policies and enforce multi-factor authentication (MFA) for all user accounts, especially administrative accounts.
Restrict access to the device's administrative interface to only trusted IP addresses or networks.
Regularly audit device configurations and logs to identify any suspicious activity.
Segment the network to limit the impact of a successful compromise. Place the device in a separate VLAN.
Disable unnecessary services and features on the device to reduce the attack surface.