MikroTik RouterOS: memory corruption flaw under attack

What is affected

MikroTik RouterOS 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.

In MikroTik RouterOS, a stack-based buffer overflow occurs when processing NetBIOS session request messages. Remote attackers with access to the service can exploit this vulnerability and gain code execution on the system.

What an attacker can do

This is a memory corruption flaw. It lets an attacker corrupt the program's memory by feeding it specially crafted content: a web page, a file or a network message. The result ranges from a crash to the attacker running their own code.

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

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

• coresecurity.comwww.coresecurity.com/core-labs/advisories/mikrotik-routeros-smb-buffer-overflow#vendor_upd
• mikrotik.commikrotik.com/download

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on September 8, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by September 29, 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 61% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.1% 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

A buffer overflow was found in the MikroTik RouterOS SMB service when processing NetBIOS session request messages. Remote attackers with access to the service can exploit this vulnerability and gain code execution on the system. The overflow occurs before authentication takes place, so it is possible for an unauthenticated remote attacker to exploit it. All architectures and all devices running RouterOS before versions 6.41.3/6.42rc27 are vulnerable.