# CVE-2025-21792: ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt

> A refcount leak in the Linux kernel AX.25 module allows local attackers to cause memory leaks and potential denial of service via socket options.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 27 Feb 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-57819, AZL-57965, BELL-CVE-2025-21792, DEBIAN-CVE-2025-21792, GHSA-pw8p-q2m4-9ch4, ROOT-OS-DEBIAN-11-CVE-2025-21792, ROOT-OS-UBUNTU-2204-CVE-2025-21792, ROOT-OS-UBUNTU-2404-CVE-2025-21792, UBUNTU-CVE-2025-21792

## What is CVE-2025-21792?

CVE-2025-21792 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 2025. 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:

ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt

If an AX25 device is bound to a socket by setting the SO_BINDTODEVICE
socket option, a refcount leak will occur in ax25_release().

Commit 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()")
added decrement of device refcounts in ax25_release(). In order for that
to work correctly the refcounts must already be incremented when the
device is bound to the socket. An AX25 device can be bound to a socket
by either calling ax25_bind() or setting SO_BINDTODEVICE socket option.
In both cases the refcounts should be incremented, but in fact it is done
only in ax25_bind().

This bug leads to the following issue reported by Syzkaller:

================================================================
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 1 PID: 5932 at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31
Modules linked in:
CPU: 1 UID: 0 PID: 5932 Comm: syz-executor424 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31
Call Trace:
 <TASK>
 __refcount_dec include/linux/refcount.h:336 [inline]
 refcount_dec include/linux/refcount.h:351 [inline]
 ref_tracker_free+0x710/0x820 lib/ref_tracker.c:236
 netdev_tracker_free include/linux/netdevice.h:4156 [inline]
 netdev_put include/linux/netdevice.h:4173 [inline]
 netdev_put include/linux/netdevice.h:4169 [inline]
 ax25_release+0x33f/0xa10 net/ax25/af_ax25.c:1069
 __sock_release+0xb0/0x270 net/socket.c:640
 sock_close+0x1c/0x30 net/socket.c:1408
 ...
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 ...
 </TASK>
================================================================

Fix the implementation of ax25_setsockopt() by adding increment of
refcounts for the new device bound, and decrement of refcounts for
the old unbound device.

## Which versions are affected by CVE-2025-21792?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21792?

Apply the vendor's patch.

## Is CVE-2025-21792 being exploited?

There is no known exploitation of CVE-2025-21792 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-2025-21792 and fix it if it is affected.

What it is: CVE-2025-21792 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 2025. 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-2025-21792 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-2025-21792/ (Markdown: https://insights.sbomify.com/CVE-2025-21792/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21792
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21792
- OSV: https://osv.dev/vulnerability/CVE-2025-21792

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21792/
Summaries are generated and may contain mistakes; the official description above is the record.