# CVE-2026-31769: gpib: fix use-after-free in IO ioctl handlers

> A use-after-free in Linux kernel GPIB ioctl handlers allows attackers to execute arbitrary code or escalate privileges via concurrent device closure.

- **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:** 1 May 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-31769, DEBIAN-CVE-2026-31769, GHSA-q8wr-mm46-444g, ROOT-OS-UBUNTU-2204-CVE-2026-31769, ROOT-OS-UBUNTU-2404-CVE-2026-31769, UBUNTU-CVE-2026-31769

## What is CVE-2026-31769?

CVE-2026-31769 is a high-severity use after free 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:

gpib: fix use-after-free in IO ioctl handlers

The IBRD, IBWRT, IBCMD, and IBWAIT ioctl handlers use a gpib_descriptor
pointer after board->big_gpib_mutex has been released.  A concurrent
IBCLOSEDEV ioctl can free the descriptor via close_dev_ioctl() during
this window, causing a use-after-free.

The IO handlers (read_ioctl, write_ioctl, command_ioctl) explicitly
release big_gpib_mutex before calling their handler.  wait_ioctl() is
called with big_gpib_mutex held, but ibwait() releases it internally
when wait_mask is non-zero.  In all four cases, the descriptor pointer
obtained from handle_to_descriptor() becomes unprotected.

Fix this by introducing a kernel-only descriptor_busy reference count
in struct gpib_descriptor.  Each handler atomically increments
descriptor_busy under file_priv->descriptors_mutex before releasing the
lock, and decrements it when done.  close_dev_ioctl() checks
descriptor_busy under the same lock and rejects the close with -EBUSY
if the count is non-zero.

A reference count rather than a simple flag is necessary because
multiple handlers can operate on the same descriptor concurrently
(e.g. IBRD and IBWAIT on the same handle from different threads).

A separate counter is needed because io_in_progress can be cleared from
unprivileged userspace via the IBWAIT ioctl (through general_ibstatus()
with set_mask containing CMPL), which would allow an attacker to bypass
a check based solely on io_in_progress.  The new descriptor_busy
counter is only modified by the kernel IO paths.

The lock ordering is consistent (big_gpib_mutex -> descriptors_mutex)
and the handlers only hold descriptors_mutex briefly during the lookup,
so there is no deadlock risk and no impact on IO throughput.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31769?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31769?

Apply the vendor's patch.

## Is CVE-2026-31769 being exploited?

There is no known exploitation of CVE-2026-31769 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-2026-31769 and fix it if it is affected.

What it is: CVE-2026-31769 is a high-severity use after free 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-2026-31769 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-2026-31769/ (Markdown: https://insights.sbomify.com/CVE-2026-31769/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31769
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31769
- OSV: https://osv.dev/vulnerability/CVE-2026-31769

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31769/
Summaries are generated and may contain mistakes; the official description above is the record.