CVE-2026-23472 serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
An infinite loop in the Linux kernel serial core causes system hangs when writing to uninitialized ports, requiring a kernel patch.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23472?
CVE-2026-23472 is a medium-severity denial of service vulnerability in Linux kernel, published on 3 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
uart_write_room() and uart_write() behave inconsistently when xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were never properly initialized):
- uart_write_room() returns kfifo_avail() which can be > 0 - uart_write() checks xmit_buf and returns 0 if NULL
This inconsistency causes an infinite loop in drivers that rely on tty_write_room() to determine if they can write:
while (tty_write_room(tty) > 0) { written = tty->ops->write(...); // written is always 0, loop never exits }
For example, caif_serial's handle_tx() enters an infinite loop when used with PORT_UNKNOWN serial ports, causing system hangs.
Fix by making uart_write_room() also check xmit_buf and return 0 if it's NULL, consistent with uart_write().
Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13
Weakness: CWE-835
Which versions are affected by CVE-2026-23472?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23472?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-23472 being exploited?
There is no known exploitation of CVE-2026-23472 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-81831, BELL-CVE-2026-23472, DEBIAN-CVE-2026-23472, GHSA-xx77-8cp4-rx22, ROOT-OS-DEBIAN-11-CVE-2026-23472, ROOT-OS-DEBIAN-12-CVE-2026-23472 and 4 more.