CVE-2026-23472: serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-03 · updated 2026-10-30
Weakness: CWE-835

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

Affected products

Linux kernel: from 2.6.12.1 before 6.18.20; from 6.19 before 6.19.10; 2.6.12-rc2, 2.6.12-rc3, 2.6.12-rc4, 2.6.12-rc5, 7.0-rc1, 7.0-rc2 (+2); 2.6.12 — fixed in 6.18.20, 6.19.10
Linux: 2.6.12 — fixed in 7.0

How to fix

Upgrade to a fixed version: Linux kernel 6.18.20, 6.19.10; Linux 7.0. Check the vendor advisory for mitigations.

References

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