# CVE-2023-52564: Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux"

> A null pointer dereference in the Linux kernel's n_gsm driver can cause a system crash, requiring a patch to revert a faulty fix.

- **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:** 2 Mar 2024
- **Updated:** 23 May 2026
- **Also known as:** BELL-CVE-2023-52564, DEBIAN-CVE-2023-52564, GHSA-g7pr-gf5r-fx64, UBUNTU-CVE-2023-52564

## What is CVE-2023-52564?

CVE-2023-52564 is a medium-severity vulnerability in Linux kernel, published on 2 Mar 2024. 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:

Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux"

This reverts commit 9b9c8195f3f0d74a826077fc1c01b9ee74907239.

The commit above is reverted as it did not solve the original issue.

gsm_cleanup_mux() tries to free up the virtual ttys by calling
gsm_dlci_release() for each available DLCI. There, dlci_put() is called to
decrease the reference counter for the DLCI via tty_port_put() which
finally calls gsm_dlci_free(). This already clears the pointer which is
being checked in gsm_cleanup_mux() before calling gsm_dlci_release().
Therefore, it is not necessary to clear this pointer in gsm_cleanup_mux()
as done in the reverted commit. The commit introduces a null pointer
dereference:
 <TASK>
 ? __die+0x1f/0x70
 ? page_fault_oops+0x156/0x420
 ? search_exception_tables+0x37/0x50
 ? fixup_exception+0x21/0x310
 ? exc_page_fault+0x69/0x150
 ? asm_exc_page_fault+0x26/0x30
 ? tty_port_put+0x19/0xa0
 gsmtty_cleanup+0x29/0x80 [n_gsm]
 release_one_tty+0x37/0xe0
 process_one_work+0x1e6/0x3e0
 worker_thread+0x4c/0x3d0
 ? __pfx_worker_thread+0x10/0x10
 kthread+0xe1/0x110
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x2f/0x50
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1b/0x30
 </TASK>

The actual issue is that nothing guards dlci_put() from being called
multiple times while the tty driver was triggered but did not yet finished
calling gsm_dlci_free().

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-52564?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-52564?

Apply the vendor's patch.

## Is CVE-2023-52564 being exploited?

There is no known exploitation of CVE-2023-52564 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-2023-52564 and fix it if it is affected.

What it is: CVE-2023-52564 is a medium-severity vulnerability in Linux kernel, published on 2 Mar 2024. 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-2023-52564 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-2023-52564/ (Markdown: https://insights.sbomify.com/CVE-2023-52564/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-52564
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-52564
- OSV: https://osv.dev/vulnerability/CVE-2023-52564

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-52564/
Summaries are generated and may contain mistakes; the official description above is the record.