# CVE-2023-54021: ext4: set goal start correctly in ext4_mb_normalize_request

> A local attacker can trigger a kernel BUG_ON crash in the ext4 filesystem via an integer underflow, causing a denial of service.

- **Severity:** Not scored
- **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:** 24 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-54021, DEBIAN-CVE-2023-54021, GHSA-xwm6-35hh-fmxm, UBUNTU-CVE-2023-54021

## What is CVE-2023-54021?

CVE-2023-54021 is a vulnerability in Linux, published on 24 Dec 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:

ext4: set goal start correctly in ext4_mb_normalize_request

We need to set ac_g_ex to notify the goal start used in
ext4_mb_find_by_goal. Set ac_g_ex instead of ac_f_ex in
ext4_mb_normalize_request.
Besides we should assure goal start is in range [first_data_block,
blocks_count) as ext4_mb_initialize_context does.

[ Added a check to make sure size is less than ar->pright; otherwise
  we could end up passing an underflowed value of ar->pright - size to
  ext4_get_group_no_and_offset(), which will trigger a BUG_ON later on.
  - TYT ]

## Which versions are affected by CVE-2023-54021?


## How do I fix CVE-2023-54021?

Apply the vendor's patch.

## Is CVE-2023-54021 being exploited?

There is no known exploitation of CVE-2023-54021 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-54021 and fix it if it is affected.

What it is: CVE-2023-54021 is a vulnerability in Linux, published on 24 Dec 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-2023-54021 in the wild and no public exploit code.

Affected product: 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-2023-54021/ (Markdown: https://insights.sbomify.com/CVE-2023-54021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-54021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-54021
- OSV: https://osv.dev/vulnerability/CVE-2023-54021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-54021/
Summaries are generated and may contain mistakes; the official description above is the record.