Linux Kernel up to 6.18.19/6.19.9/7.0-rc4 serial handle_tx infinite loop

Summaryinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.18.19/6.19.9/7.0-rc4. Impacted is the function handle_tx of the component serial. The manipulation results in infinite loop. This vulnerability is known as CVE-2026-23472. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.18.19/6.19.9/7.0-rc4. Affected is the function handle_tx of the component serial. The manipulation with an unknown input leads to a infinite loop vulnerability. CWE is classifying the issue as CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. This is going to have an impact on availability. CVE summarizes:

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

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-23472 since 01/13/2026. There are known technical details, but no exploit is available.

Upgrading to version 6.18.20, 6.19.10 or 7.0-rc5 eliminates this vulnerability. Applying the patch efe85a557186b7fe915572ae93a8f3f78bfd9a22/bc70f2b36cf474d5cc8ecbcaf57f3e326fdec67c/455ce986fa356ff43a43c0d363ba95fa152f21d5 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.18.8
• 6.18.9
• 6.18.10
• 6.18.11
• 6.18.12
• 6.18.13
• 6.18.14
• 6.18.15
• 6.18.16
• 6.18.17
• 6.18.18
• 6.18.19
• 6.19.0
• 6.19.1
• 6.19.2
• 6.19.3
• 6.19.4
• 6.19.5
• 6.19.6
• 6.19.7
• 6.19.8
• 6.19.9
• 7.0-rc1
• 7.0-rc2
• 7.0-rc3
• 7.0-rc4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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