# CVE-2025-40275: ALSA: usb-audio: Fix NULL pointer dereference in snd_usb_mixer_controls_badd

> A local attacker with physical access can cause a kernel crash by connecting a malicious USB audio device due to a missing NULL check.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 6 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40275, DEBIAN-CVE-2025-40275, GHSA-x49w-vx84-7x88, ROOT-OS-DEBIAN-12-CVE-2025-40275, ROOT-OS-DEBIAN-13-CVE-2025-40275, ROOT-OS-UBUNTU-2204-CVE-2025-40275, ROOT-OS-UBUNTU-2404-CVE-2025-40275, UBUNTU-CVE-2025-40275

## What is CVE-2025-40275?

CVE-2025-40275 is a vulnerability in Linux, published on 6 Dec 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ALSA: usb-audio: Fix NULL pointer dereference in snd_usb_mixer_controls_badd

In snd_usb_create_streams(), for UAC version 3 devices, the Interface
Association Descriptor (IAD) is retrieved via usb_ifnum_to_if(). If this
call fails, a fallback routine attempts to obtain the IAD from the next
interface and sets a BADD profile. However, snd_usb_mixer_controls_badd()
assumes that the IAD retrieved from usb_ifnum_to_if() is always valid,
without performing a NULL check. This can lead to a NULL pointer
dereference when usb_ifnum_to_if() fails to find the interface descriptor.

This patch adds a NULL pointer check after calling usb_ifnum_to_if() in
snd_usb_mixer_controls_badd() to prevent the dereference.

This issue was discovered by syzkaller, which triggered the bug by sending
a crafted USB device descriptor.

## Which versions are affected by CVE-2025-40275?


## How do I fix CVE-2025-40275?

Apply the vendor's patch.

## Is CVE-2025-40275 being exploited?

There is no known exploitation of CVE-2025-40275 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40275 and fix it if it is affected.

What it is: CVE-2025-40275 is a vulnerability in Linux, published on 6 Dec 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-40275 in the wild and no public exploit code.

Affected product: Linux. 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-2025-40275/ (Markdown: https://insights.sbomify.com/CVE-2025-40275/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40275
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40275
- OSV: https://osv.dev/vulnerability/CVE-2025-40275

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40275/
Summaries are generated and may contain mistakes; the official description above is the record.