# CVE-2026-90151: NFSv4: remove callback IDR entry on client allocation failure

> A use-after-free vulnerability in the Linux kernel NFSv4 client allows attackers to trigger memory corruption and potentially execute code or escalate privileges.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 19 Oct 2026
- **Also known as:** AZL-102821, BELL-CVE-2026-90151, DEBIAN-CVE-2026-90151, GHSA-h72c-5c39-xm46, UBUNTU-CVE-2026-90151

## What is CVE-2026-90151?

CVE-2026-90151 is a critical use after free 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:

NFSv4: remove callback IDR entry on client allocation failure

nfs4_alloc_client() allocates an NFSv4.0 callback identifier before it
finishes setting up the client. If any later initialization step fails,
the error path frees the nfs_client directly with nfs_free_client(). That
bypasses nfs_put_client(), which is where the callback IDR entry is
removed during normal teardown.

A failed allocation can therefore leave cb_ident_idr pointing at a freed
nfs_client. A later NFSv4.0 callback lookup by cb_ident would find the
stale pointer and take a reference to it.

Make the callback IDR removal helper callable by the allocation failure
path, and remove the callback identifier before freeing the client.

This was found by a local static-analysis checker for publish-before-free
lifetime bugs and confirmed by manual inspection.

## Which versions are affected by CVE-2026-90151?


## How do I fix CVE-2026-90151?

Apply the vendor's patch.

## Is CVE-2026-90151 being exploited?

There is no known exploitation of CVE-2026-90151 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90151 and fix it if it is affected.

What it is: CVE-2026-90151 is a critical use after free 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-2026-90151 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-2026-90151/ (Markdown: https://insights.sbomify.com/CVE-2026-90151/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90151
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90151
- OSV: https://osv.dev/vulnerability/CVE-2026-90151

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90151/
Summaries are generated and may contain mistakes; the official description above is the record.