Zyxel DSL CPE Devices: code execution flaw under attack

What is affected

Zyxel DSL CPE Devices are the kind of equipment many homes and small offices run for years without touching: a router, camera or storage box. Attackers scan the internet for exposed units, and a hijacked one can spy on traffic or be enrolled in a botnet without any visible sign.

Multiple Zyxel DSL CPE devices contain a post-authentication command injection vulnerability in the management commands that could allow an authenticated attacker to execute OS commands via Telnet.

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached

Over the internet or network

Access the attacker needs

A basic user account

Does the victim have to do something?

No, works without the victim doing anything

What to do

1. Check whether you own this device: look at the label on your router, camera or NAS, or open its admin page and note the model and firmware version.
2. Install the latest firmware from the manufacturer's support page or the device's own update menu.
3. If the manufacturer no longer releases updates for the model, replace it. An end-of-life device with an exploited flaw cannot be made safe.
4. Turn off remote administration from the internet unless you truly need it, and change the default admin password.

The impacted product could be end-of-life (EoL) and/or end-of-service (EoS). Users should discontinue product utilization if a current mitigation is unavailable.

Vendor advisories and fixes

• zyxel.comwww.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-command-in
• zyxel.comwww.zyxel.com/service-provider/global/en/security-advisories/zyxel-security-advisory-comma

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on February 11, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by March 4, 2025, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 22% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 98% of all scored vulnerabilities.

Its CVSS severity score is 8.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

**UNSUPPORTED WHEN ASSIGNED** A post-authentication command injection vulnerability in the management commands of the legacy DSL CPE Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 could allow an authenticated attacker to execute operating system (OS) commands on an affected device via Telnet.