# CVE-2025-68240: nilfs2: avoid having an active sc_timer before freeing sci

> A use-after-free vulnerability in the Linux kernel nilfs2 filesystem allows local attackers to cause a denial of service via improper timer shutdown.

- **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:** 16 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-68240, DEBIAN-CVE-2025-68240, GHSA-m6q3-c8gp-2rp9, ROOT-OS-DEBIAN-13-CVE-2025-68240, UBUNTU-CVE-2025-68240

## What is CVE-2025-68240?

CVE-2025-68240 is an use after free vulnerability in Linux, published on 16 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:

nilfs2: avoid having an active sc_timer before freeing sci

Because kthread_stop did not stop sc_task properly and returned -EINTR,
the sc_timer was not properly closed, ultimately causing the problem [1]
reported by syzbot when freeing sci due to the sc_timer not being closed.

Because the thread sc_task main function nilfs_segctor_thread() returns 0
when it succeeds, when the return value of kthread_stop() is not 0 in
nilfs_segctor_destroy(), we believe that it has not properly closed
sc_timer.

We use timer_shutdown_sync() to sync wait for sc_timer to shutdown, and
set the value of sc_task to NULL under the protection of lock
sc_state_lock, so as to avoid the issue caused by sc_timer not being
properly shutdowned.

[1]
ODEBUG: free active (active state 0) object: 00000000dacb411a object type: timer_list hint: nilfs_construction_timeout
Call trace:
 nilfs_segctor_destroy fs/nilfs2/segment.c:2811 [inline]
 nilfs_detach_log_writer+0x668/0x8cc fs/nilfs2/segment.c:2877
 nilfs_put_super+0x4c/0x12c fs/nilfs2/super.c:509

## Which versions are affected by CVE-2025-68240?


## How do I fix CVE-2025-68240?

Apply the vendor's patch.

## Is CVE-2025-68240 being exploited?

There is no known exploitation of CVE-2025-68240 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68240 and fix it if it is affected.

What it is: CVE-2025-68240 is an use after free vulnerability in Linux, published on 16 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-2025-68240 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-2025-68240/ (Markdown: https://insights.sbomify.com/CVE-2025-68240/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68240
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68240
- OSV: https://osv.dev/vulnerability/CVE-2025-68240

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68240/
Summaries are generated and may contain mistakes; the official description above is the record.