# CVE-2026-90149: NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers

> A NULL pointer dereference in the Linux kernel NFSv4 flexfiles module causes a system crash when interacting with NFSv4.0 data servers.

- **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-102438, BELL-CVE-2026-90149, DEBIAN-CVE-2026-90149, GHSA-5pv5-p9q3-rvv6, UBUNTU-CVE-2026-90149

## What is CVE-2026-90149?

CVE-2026-90149 is a high-severity 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/flexfiles: fix NULL dereference for NFSv4.0 data servers

flexfiles accepts NFSv4.0 data servers, but two NFSv4 code paths assume
the data server client has a session. Unlike NFSv4.1+, an NFSv4.0 client
has no session (clp->cl_session is NULL; it uses clp->cl_slot_tbl), so
I/O to a v4.0 flexfiles DS oopses:

  - nfs4_init_ds_session() dereferences clp->cl_session->session_state
    while seeding the DS lease. It also only seeds cl_lease_time when
    NFS4_SESSION_INITING is set; without a session that never happens, so
    cl_lease_time stays 0 and nfs4_renew_state() busy-loops, requeuing
    every 5 seconds. Seed the lease whenever there is no session and
    return before touching session state.

  - ff_layout_async_handle_error_v4() dereferences
    clp->cl_session->fc_slot_table on every DS I/O error. Fall back to the
    v4.0 transport slot table (clp->cl_slot_tbl) when there is no session.

## Which versions are affected by CVE-2026-90149?


## How do I fix CVE-2026-90149?

Apply the vendor's patch.

## Is CVE-2026-90149 being exploited?

There is no known exploitation of CVE-2026-90149 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90149 and fix it if it is affected.

What it is: CVE-2026-90149 is a high-severity 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-2026-90149 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-2026-90149/ (Markdown: https://insights.sbomify.com/CVE-2026-90149/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90149
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90149
- OSV: https://osv.dev/vulnerability/CVE-2026-90149

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90149/
Summaries are generated and may contain mistakes; the official description above is the record.