# CVE-2026-90234: NFS: Return a delegation the client fails to record

> A flaw in the Linux kernel NFS client causes a denial of service by failing to return delegations, leading to infinite state manager loops.

- **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:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102395, BELL-CVE-2026-90234, DEBIAN-CVE-2026-90234, GHSA-qx9f-2gch-8fvp, UBUNTU-CVE-2026-90234

## What is CVE-2026-90234?

CVE-2026-90234 is a high-severity denial of service vulnerability in Linux, published on 17 Sep 2026. 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:

NFS: Return a delegation the client fails to record

When an NFS server grants a delegation in an OPEN reply,
nfs_inode_set_delegation() records it on the client. However, three
of its error flows return without sending DELEGRETURN.

A delegation can be relinquished only by DELEGRETURN (RFC 8881
Section 20.2.4), so dropping one silently leaves the server believing
the client still holds it. If the server happens to recall that
delegation, the client answers CB_RECALL with NFS4ERR_BADHANDLE
because it has no record of the stateid. The server revokes the
delegation and moves it onto its cl_revoked list, because the client
never sends the FREE_STATEID that would drain it. Every subsequent
SEQUENCE reply then carries SEQ4_STATUS_RECALLABLE_STATE_REVOKED,
and the client's state manager loops issuing TEST_STATEID across its
delegations without ever clearing the condition.

The window is easy to reach now that a server offers a write
delegation on any write OPEN: a delegation recalled for one opener
races a re-open that the server answers with a fresh write
delegation.

Instead of dropping it, hand the delegation back during these error
flows.

## Which versions are affected by CVE-2026-90234?


## How do I fix CVE-2026-90234?

Apply the vendor's patch.

## Is CVE-2026-90234 being exploited?

There is no known exploitation of CVE-2026-90234 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90234 and fix it if it is affected.

What it is: CVE-2026-90234 is a high-severity denial of service vulnerability in Linux, published on 17 Sep 2026. 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-2026-90234 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-2026-90234/ (Markdown: https://insights.sbomify.com/CVE-2026-90234/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90234
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90234
- OSV: https://osv.dev/vulnerability/CVE-2026-90234

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90234/
Summaries are generated and may contain mistakes; the official description above is the record.