# CVE-2026-31458: mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

> Privileged users can trigger a NULL pointer dereference in the Linux kernel DAMON subsystem by setting context count to zero, causing a denial of service.

- **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:** 22 Apr 2026
- **Updated:** 11 May 2026
- **Also known as:** AZL-83228, BELL-CVE-2026-31458, DEBIAN-CVE-2026-31458, GHSA-rhx5-38hr-wvr9, ROOT-OS-DEBIAN-12-CVE-2026-31458, ROOT-OS-DEBIAN-13-CVE-2026-31458, ROOT-OS-UBUNTU-2404-CVE-2026-31458, UBUNTU-CVE-2026-31458

## What is CVE-2026-31458?

CVE-2026-31458 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 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:

mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

Multiple sysfs command paths dereference contexts_arr[0] without first
verifying that kdamond->contexts->nr == 1.  A user can set nr_contexts to
0 via sysfs while DAMON is running, causing NULL pointer dereferences.

In more detail, the issue can be triggered by privileged users like
below.

First, start DAMON and make contexts directory empty
(kdamond->contexts->nr == 0).

    # damo start
    # cd /sys/kernel/mm/damon/admin/kdamonds/0
    # echo 0 > contexts/nr_contexts

Then, each of below commands will cause the NULL pointer dereference.

    # echo update_schemes_stats > state
    # echo update_schemes_tried_regions > state
    # echo update_schemes_tried_bytes > state
    # echo update_schemes_effective_quotas > state
    # echo update_tuned_intervals > state

Guard all commands (except OFF) at the entry point of
damon_sysfs_handle_cmd().

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-31458?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31458?

Apply the vendor's patch.

## Is CVE-2026-31458 being exploited?

There is no known exploitation of CVE-2026-31458 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-2026-31458 and fix it if it is affected.

What it is: CVE-2026-31458 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 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-2026-31458 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-2026-31458/ (Markdown: https://insights.sbomify.com/CVE-2026-31458/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31458
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31458
- OSV: https://osv.dev/vulnerability/CVE-2026-31458

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31458/
Summaries are generated and may contain mistakes; the official description above is the record.