TP-Link Archer AX21: code execution flaw under attack

What is affected

TP-Link Archer AX21 is 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.

TP-Link Archer AX-21 contains a command injection vulnerability that allows for remote code execution.

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

From the same local network

Access the attacker needs

No account needed

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.

Apply updates per vendor instructions.

Vendor advisories and fixes

• tp-link.comwww.tp-link.com/us/support/download/archer-ax21/v3/#Firmware

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on May 1, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 22, 2023, 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 100% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 100.0% 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

TP-Link Archer AX21 (AX1800) firmware versions before 1.1.4 Build 20230219 contained a command injection vulnerability in the country form of the /cgi-bin/luci;stok=/locale endpoint on the web management interface. Specifically, the country parameter of the write operation was not sanitized before being used in a call to popen(), allowing an unauthenticated attacker to inject commands, which would be run as root, with a simple POST request.