Linux Kernel: memory corruption flaw under attack

What is affected

Linux Kernel is found on ordinary personal computers and phones, so this is not only a problem for companies. If you use it and have not updated since the fix was released, you are exposed.

Linux Kernel contains a race condition vulnerability within the n_tty_write function that allows local users to cause a denial-of-service (DoS) or gain privileges via read and write operations with long strings.

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

Needs access to the device or a file opened on it

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. Update Linux Kernel now. Open the update or "About" screen, install whatever is offered and restart the app or device, because the fix is not active until you do.
2. Turn on automatic updates so the next fix arrives without you having to look for it.
3. If your device is too old to receive this update, stop using the affected app for anything sensitive and plan a replacement.

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

Vendor advisories and fixes

• lkml.iu.edulkml.iu.edu/hypermail/linux/kernel/1609.1/02103.html

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on May 12, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by June 2, 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 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 5.5 out of 10 (medium), as recorded in the US National Vulnerability Database.

Technical description

The n_tty_write function in drivers/tty/n_tty.c in the Linux kernel through 3.14.3 does not properly manage tty driver access in the "LECHO & !OPOST" case, which allows local users to cause a denial of service (memory corruption and system crash) or gain privileges by triggering a race condition involving read and write operations with long strings.