# CVE-2026-31778: ALSA: caiaq: fix stack out-of-bounds read in init_card

> A stack out-of-bounds read in the Linux kernel ALSA caiaq driver allows attackers with physical access to leak stack memory or cause a crash via a malicious USB device.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 1 May 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31778, DEBIAN-CVE-2026-31778, GHSA-87f3-mhhq-wfvx, ROOT-OS-DEBIAN-11-CVE-2026-31778, ROOT-OS-UBUNTU-2204-CVE-2026-31778, ROOT-OS-UBUNTU-2404-CVE-2026-31778, UBUNTU-CVE-2026-31778

## What is CVE-2026-31778?

CVE-2026-31778 is a high-severity memory corruption vulnerability in Linux kernel, published on 1 May 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:

ALSA: caiaq: fix stack out-of-bounds read in init_card

The loop creates a whitespace-stripped copy of the card shortname
where `len < sizeof(card->id)` is used for the bounds check. Since
sizeof(card->id) is 16 and the local id buffer is also 16 bytes,
writing 16 non-space characters fills the entire buffer,
overwriting the terminating nullbyte.

When this non-null-terminated string is later passed to
snd_card_set_id() -> copy_valid_id_string(), the function scans
forward with `while (*nid && ...)` and reads past the end of the
stack buffer, reading the contents of the stack.

A USB device with a product name containing many non-ASCII, non-space
characters (e.g. multibyte UTF-8) will reliably trigger this as follows:

  BUG: KASAN: stack-out-of-bounds in copy_valid_id_string
       sound/core/init.c:696 [inline]
  BUG: KASAN: stack-out-of-bounds in snd_card_set_id_no_lock+0x698/0x74c
       sound/core/init.c:718

The off-by-one has been present since commit bafeee5b1f8d ("ALSA:
snd_usb_caiaq: give better shortname") from June 2009 (v2.6.31-rc1),
which first introduced this whitespace-stripping loop. The original
code never accounted for the null terminator when bounding the copy.

Fix this by changing the loop bound to `sizeof(card->id) - 1`,
ensuring at least one byte remains as the null terminator.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-31778?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31778?

Apply the vendor's patch.

## Is CVE-2026-31778 being exploited?

There is no known exploitation of CVE-2026-31778 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-2026-31778 and fix it if it is affected.

What it is: CVE-2026-31778 is a high-severity memory corruption vulnerability in Linux kernel, published on 1 May 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-2026-31778 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-2026-31778/ (Markdown: https://insights.sbomify.com/CVE-2026-31778/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31778
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31778
- OSV: https://osv.dev/vulnerability/CVE-2026-31778

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31778/
Summaries are generated and may contain mistakes; the official description above is the record.