# CVE-2026-53043: ocfs2/dlm: validate qr_numregions in dlm_match_regions()

> A missing bounds check in the Linux kernel OCFS2 DLM allows out-of-bounds reads via crafted network messages, potentially causing crashes or data leaks.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-53043, DEBIAN-CVE-2026-53043, GHSA-hv9w-qqh8-9pfh, ROOT-OS-DEBIAN-11-CVE-2026-53043, ROOT-OS-DEBIAN-12-CVE-2026-53043, ROOT-OS-UBUNTU-2204-CVE-2026-53043, ROOT-OS-UBUNTU-2404-CVE-2026-53043, UBUNTU-CVE-2026-53043

## What is CVE-2026-53043?

CVE-2026-53043 is a critical memory corruption vulnerability in Linux kernel, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ocfs2/dlm: validate qr_numregions in dlm_match_regions()

Patch series "ocfs2/dlm: fix two bugs in dlm_match_regions()".

In dlm_match_regions(), the qr_numregions field from a DLM_QUERY_REGION
network message is used to drive loops over the qr_regions buffer without
sufficient validation.  This series fixes two issues:

- Patch 1 adds a bounds check to reject messages where qr_numregions
  exceeds O2NM_MAX_REGIONS. The o2net layer only validates message
  byte length; it does not constrain field values, so a crafted message
  can set qr_numregions up to 255 and trigger out-of-bounds reads past
  the 1024-byte qr_regions buffer.

- Patch 2 fixes an off-by-one in the local-vs-remote comparison loop,
  which uses '<=' instead of '<', reading one entry past the valid range
  even when qr_numregions is within bounds.

This patch (of 2):

The qr_numregions field from a DLM_QUERY_REGION network message is used
directly as loop bounds in dlm_match_regions() without checking against
O2NM_MAX_REGIONS.  Since qr_regions is sized for at most O2NM_MAX_REGIONS
(32) entries, a crafted message with qr_numregions > 32 causes
out-of-bounds reads past the qr_regions buffer.

Add a bounds check for qr_numregions before entering the loops.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-53043?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53043?

Apply the vendor's patch.

## Is CVE-2026-53043 being exploited?

There is no known exploitation of CVE-2026-53043 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-2026-53043 and fix it if it is affected.

What it is: CVE-2026-53043 is a critical memory corruption vulnerability in Linux kernel, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53043 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-2026-53043/ (Markdown: https://insights.sbomify.com/CVE-2026-53043/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53043
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53043
- OSV: https://osv.dev/vulnerability/CVE-2026-53043

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53043/
Summaries are generated and may contain mistakes; the official description above is the record.