# CVE-2025-40326: NFSD: Define actions for the new time_deleg FATTR4 attributes

> A flaw in the Linux kernel's NFS server could cause a crash when handling invalid GETATTR requests for new time_deleg attributes.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40326, DEBIAN-CVE-2025-40326, GHSA-3c64-vv99-p2qr, UBUNTU-CVE-2025-40326

## What is CVE-2025-40326?

CVE-2025-40326 is a high-severity denial of service vulnerability in Linux, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Define actions for the new time_deleg FATTR4 attributes

NFSv4 clients won't send legitimate GETATTR requests for these new
attributes because they are intended to be used only with CB_GETATTR
and SETATTR. But NFSD has to do something besides crashing if it
ever sees a GETATTR request that queries these attributes.

RFC 8881 Section 18.7.3 states:

> The server MUST return a value for each attribute that the client
> requests if the attribute is supported by the server for the
> target file system. If the server does not support a particular
> attribute on the target file system, then it MUST NOT return the
> attribute value and MUST NOT set the attribute bit in the result
> bitmap. The server MUST return an error if it supports an
> attribute on the target but cannot obtain its value. In that case,
> no attribute values will be returned.

Further, RFC 9754 Section 5 states:

> These new attributes are invalid to be used with GETATTR, VERIFY,
> and NVERIFY, and they can only be used with CB_GETATTR and SETATTR
> by a client holding an appropriate delegation.

Thus there does not appear to be a specific server response mandated
by specification. Taking the guidance that querying these attributes
via GETATTR is "invalid", NFSD will return nfserr_inval, failing the
request entirely.

## Which versions are affected by CVE-2025-40326?


## How do I fix CVE-2025-40326?

Apply the vendor's patch.

## Is CVE-2025-40326 being exploited?

There is no known exploitation of CVE-2025-40326 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40326 and fix it if it is affected.

What it is: CVE-2025-40326 is a high-severity denial of service vulnerability in Linux, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40326 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-2025-40326/ (Markdown: https://insights.sbomify.com/CVE-2025-40326/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40326
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40326
- OSV: https://osv.dev/vulnerability/CVE-2025-40326

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40326/
Summaries are generated and may contain mistakes; the official description above is the record.