# CVE-2026-72225: jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()

> An integer underflow in the Linux kernel's jbd2 journal initialization can lead to journal corruption and system abort, causing denial of service.

- **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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72225, DEBIAN-CVE-2026-72225, GHSA-rm6f-75fw-gq38, UBUNTU-CVE-2026-72225

## What is CVE-2026-72225?

CVE-2026-72225 is a high-severity vulnerability in Linux, published on 15 Aug 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:

jbd2: fix integer underflow in jbd2_journal_initialize_fast_commit()

jbd2_journal_initialize_fast_commit() validates journal capacity by
checking (journal->j_last - num_fc_blks < JBD2_MIN_JOURNAL_BLOCKS).
Both j_last and num_fc_blks are unsigned, so when num_fc_blks exceeds
j_last the subtraction wraps to a large value, bypassing the bounds
check.

The resulting underflow corrupts j_last, j_fc_first, and j_free,
leading to journal abort.

Fix by checking num_fc_blks against j_last before the subtraction,
returning -EFSCORRUPTED.

## Which versions are affected by CVE-2026-72225?


## How do I fix CVE-2026-72225?

Apply the vendor's patch.

## Is CVE-2026-72225 being exploited?

There is no known exploitation of CVE-2026-72225 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72225 and fix it if it is affected.

What it is: CVE-2026-72225 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72225 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-2026-72225/ (Markdown: https://insights.sbomify.com/CVE-2026-72225/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72225
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72225
- OSV: https://osv.dev/vulnerability/CVE-2026-72225

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72225/
Summaries are generated and may contain mistakes; the official description above is the record.