Dasan Gigabit Passive Optical Network (GPON) Routers: code execution flaw under attack

What is affected

Dasan Gigabit Passive Optical Network (GPON) Routers 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.

Dasan GPON Routers contain an authentication bypass vulnerability. When combined with CVE-2018-10561, exploitation can allow an attacker to perform 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

Over the internet or network

Access the attacker needs

No account needed

Does the victim have to do something?

No, works without the victim doing anything

CISA records this vulnerability as known to be used in ransomware campaigns: attackers use it to get in, then encrypt files and demand payment.

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 is end-of-life and should be disconnected if still in use.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on March 31, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by April 21, 2022, 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 9.8 out of 10 (critical), as recorded in the US National Vulnerability Database.

Technical description

An issue was discovered on Dasan GPON home routers. Command Injection can occur via the dest_host parameter in a diag_action=ping request to a GponForm/diag_Form URI. Because the router saves ping results in /tmp and transmits them to the user when the user revisits /diag.html, it's quite simple to execute commands and retrieve their output.