# CVE-2025-71237: nilfs2: Fix potential block overflow that cause system hang

> An integer underflow in the nilfs2 filesystem allows a local user to cause a system hang via the FITRIM command.

- **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:** 18 Feb 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-71237, DEBIAN-CVE-2025-71237, GHSA-m34c-wrf8-mw69, ROOT-OS-DEBIAN-11-CVE-2025-71237, ROOT-OS-DEBIAN-12-CVE-2025-71237, ROOT-OS-UBUNTU-2204-CVE-2025-71237, ROOT-OS-UBUNTU-2404-CVE-2025-71237, UBUNTU-CVE-2025-71237

## What is CVE-2025-71237?

CVE-2025-71237 is a medium-severity vulnerability in Linux kernel, published on 18 Feb 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:

nilfs2: Fix potential block overflow that cause system hang

When a user executes the FITRIM command, an underflow can occur when
calculating nblocks if end_block is too small. Since nblocks is of
type sector_t, which is u64, a negative nblocks value will become a
very large positive integer. This ultimately leads to the block layer
function __blkdev_issue_discard() taking an excessively long time to
process the bio chain, and the ns_segctor_sem lock remains held for a
long period. This prevents other tasks from acquiring the ns_segctor_sem
lock, resulting in the hang reported by syzbot in [1].

If the ending block is too small, typically if it is smaller than 4KiB
range, depending on the usage of the segment 0, it may be possible to
attempt a discard request beyond the device size causing the hang.

Exiting successfully and assign the discarded size (0 in this case)
to range->len.

Although the start and len values in the user input range are too small,
a conservative strategy is adopted here to safely ignore them, which is
equivalent to a no-op; it will not perform any trimming and will not
throw an error.

[1]
task:segctord state:D stack:28968 pid:6093 tgid:6093  ppid:2 task_flags:0x200040 flags:0x00080000
Call Trace:
 rwbase_write_lock+0x3dd/0x750 kernel/locking/rwbase_rt.c:272
 nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357
 nilfs_segctor_thread_construct fs/nilfs2/segment.c:2569 [inline]
 nilfs_segctor_thread+0x6ec/0xe00 fs/nilfs2/segment.c:2684

[ryusuke: corrected part of the commit message about the consequences]

## Which versions are affected by CVE-2025-71237?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-71237?

Apply the vendor's patch.

## Is CVE-2025-71237 being exploited?

There is no known exploitation of CVE-2025-71237 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-2025-71237 and fix it if it is affected.

What it is: CVE-2025-71237 is a medium-severity vulnerability in Linux kernel, published on 18 Feb 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-2025-71237 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-2025-71237/ (Markdown: https://insights.sbomify.com/CVE-2025-71237/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-71237
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-71237
- OSV: https://osv.dev/vulnerability/CVE-2025-71237

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-71237/
Summaries are generated and may contain mistakes; the official description above is the record.