# CVE-2025-38480: comedi: Fix use of uninitialized data in insn_rw_emulate_bits()

> A local attacker can read uninitialized kernel memory or write invalid data to digital output channels via the comedi subsystem.

- **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:** 28 Jul 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-65898, BELL-CVE-2025-38480, DEBIAN-CVE-2025-38480, GHSA-g4qg-7mgj-p8v6, ROOT-OS-DEBIAN-11-CVE-2025-38480, ROOT-OS-DEBIAN-12-CVE-2025-38480, ROOT-OS-UBUNTU-2204-CVE-2025-38480, ROOT-OS-UBUNTU-2404-CVE-2025-38480, UBUNTU-CVE-2025-38480

## What is CVE-2025-38480?

CVE-2025-38480 is a medium-severity vulnerability in Debian Debian Linux, published on 28 Jul 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:

comedi: Fix use of uninitialized data in insn_rw_emulate_bits()

For Comedi `INSN_READ` and `INSN_WRITE` instructions on "digital"
subdevices (subdevice types `COMEDI_SUBD_DI`, `COMEDI_SUBD_DO`, and
`COMEDI_SUBD_DIO`), it is common for the subdevice driver not to have
`insn_read` and `insn_write` handler functions, but to have an
`insn_bits` handler function for handling Comedi `INSN_BITS`
instructions.  In that case, the subdevice's `insn_read` and/or
`insn_write` function handler pointers are set to point to the
`insn_rw_emulate_bits()` function by `__comedi_device_postconfig()`.

For `INSN_WRITE`, `insn_rw_emulate_bits()` currently assumes that the
supplied `data[0]` value is a valid copy from user memory.  It will at
least exist because `do_insnlist_ioctl()` and `do_insn_ioctl()` in
"comedi_fops.c" ensure at lease `MIN_SAMPLES` (16) elements are
allocated.  However, if `insn->n` is 0 (which is allowable for
`INSN_READ` and `INSN_WRITE` instructions, then `data[0]` may contain
uninitialized data, and certainly contains invalid data, possibly from a
different instruction in the array of instructions handled by
`do_insnlist_ioctl()`.  This will result in an incorrect value being
written to the digital output channel (or to the digital input/output
channel if configured as an output), and may be reflected in the
internal saved state of the channel.

Fix it by returning 0 early if `insn->n` is 0, before reaching the code
that accesses `data[0]`.  Previously, the function always returned 1 on
success, but it is supposed to be the number of data samples actually
read or written up to `insn->n`, which is 0 in this case.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2025-38480?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38480?

Apply the vendor's patch.

## Is CVE-2025-38480 being exploited?

There is no known exploitation of CVE-2025-38480 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38480 and fix it if it is affected.

What it is: CVE-2025-38480 is a medium-severity vulnerability in Debian Debian Linux, published on 28 Jul 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-2025-38480 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-38480/ (Markdown: https://insights.sbomify.com/CVE-2025-38480/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38480
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38480
- OSV: https://osv.dev/vulnerability/CVE-2025-38480

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38480/
Summaries are generated and may contain mistakes; the official description above is the record.