# 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.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** Yes
- **Published:** 3 Apr 2026
- **Updated:** 21 Oct 2026
- **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, ROOT-OS-DEBIAN-13-CVE-2026-23472, ROOT-OS-UBUNTU-2204-CVE-2026-23472, ROOT-OS-UBUNTU-2404-CVE-2026-23472, UBUNTU-CVE-2026-23472

## 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 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-23472?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23472?

Apply the vendor's patch.

## 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

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23472 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-23472 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23472/ (Markdown: https://insights.sbomify.com/CVE-2026-23472/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23472
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23472
- OSV: https://osv.dev/vulnerability/CVE-2026-23472

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23472/
Summaries are generated and may contain mistakes; the official description above is the record.