# CVE-2025-40105: vfs: Don't leak disconnected dentries on umount

> A Linux kernel vulnerability allows attackers to cause a denial of service by triggering a memory leak that prevents unmounting filesystems.

- **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:** 30 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-69421, BELL-CVE-2025-40105, DEBIAN-CVE-2025-40105, GHSA-9wgm-cmcc-8467, ROOT-OS-DEBIAN-11-CVE-2025-40105, ROOT-OS-DEBIAN-12-CVE-2025-40105, ROOT-OS-DEBIAN-13-CVE-2025-40105, ROOT-OS-UBUNTU-2204-CVE-2025-40105, ROOT-OS-UBUNTU-2404-CVE-2025-40105, UBUNTU-CVE-2025-40105

## What is CVE-2025-40105?

CVE-2025-40105 is a high-severity denial of service vulnerability in Linux, published on 30 Oct 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:

vfs: Don't leak disconnected dentries on umount

When user calls open_by_handle_at() on some inode that is not cached, we
will create disconnected dentry for it. If such dentry is a directory,
exportfs_decode_fh_raw() will then try to connect this dentry to the
dentry tree through reconnect_path(). It may happen for various reasons
(such as corrupted fs or race with rename) that the call to
lookup_one_unlocked() in reconnect_one() will fail to find the dentry we
are trying to reconnect and instead create a new dentry under the
parent. Now this dentry will not be marked as disconnected although the
parent still may well be disconnected (at least in case this
inconsistency happened because the fs is corrupted and .. doesn't point
to the real parent directory). This creates inconsistency in
disconnected flags but AFAICS it was mostly harmless. At least until
commit f1ee616214cb ("VFS: don't keep disconnected dentries on d_anon")
which removed adding of most disconnected dentries to sb->s_anon list.
Thus after this commit cleanup of disconnected dentries implicitely
relies on the fact that dput() will immediately reclaim such dentries.
However when some leaf dentry isn't marked as disconnected, as in the
scenario described above, the reclaim doesn't happen and the dentries
are "leaked". Memory reclaim can eventually reclaim them but otherwise
they stay in memory and if umount comes first, we hit infamous "Busy
inodes after unmount" bug. Make sure all dentries created under a
disconnected parent are marked as disconnected as well.

## Which versions are affected by CVE-2025-40105?


## How do I fix CVE-2025-40105?

Apply the vendor's patch.

## Is CVE-2025-40105 being exploited?

There is no known exploitation of CVE-2025-40105 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40105 and fix it if it is affected.

What it is: CVE-2025-40105 is a high-severity denial of service vulnerability in Linux, published on 30 Oct 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-2025-40105 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-2025-40105/ (Markdown: https://insights.sbomify.com/CVE-2025-40105/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40105
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40105
- OSV: https://osv.dev/vulnerability/CVE-2025-40105

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40105/
Summaries are generated and may contain mistakes; the official description above is the record.