# CVE-2026-90104: NFSv4.1: zero referring call lists before decoding

> An attacker can trigger a use-after-free in the Linux kernel NFSv4.1 callback handler by sending crafted packets, potentially causing a crash or code execution.

- **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:** 21 Oct 2026
- **Also known as:** AZL-102090, BELL-CVE-2026-90104, DEBIAN-CVE-2026-90104, GHSA-8hhg-gc4j-p2q8, UBUNTU-CVE-2026-90104

## What is CVE-2026-90104?

CVE-2026-90104 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:

NFSv4.1: zero referring call lists before decoding

decode_cb_sequence_args() allocates csa_rclists with kmalloc_objs(), so
each referring_call_list starts uninitialized. decode_rc_list() assigns
rcl_refcalls only when rcl_nrefcalls is nonzero. A valid list with zero
referring calls therefore leaves the pointer uninitialized, and
nfs4_callback_sequence() later passes stale slab contents to kfree().

Allocate csa_rclists with kzalloc_objs() so every rcl_refcalls member is
NULL from the beginning, including valid empty referring call lists.

## Which versions are affected by CVE-2026-90104?


## How do I fix CVE-2026-90104?

Apply the vendor's patch.

## Is CVE-2026-90104 being exploited?

There is no known exploitation of CVE-2026-90104 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90104 and fix it if it is affected.

What it is: CVE-2026-90104 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-2026-90104 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-2026-90104/ (Markdown: https://insights.sbomify.com/CVE-2026-90104/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90104
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90104
- OSV: https://osv.dev/vulnerability/CVE-2026-90104

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90104/
Summaries are generated and may contain mistakes; the official description above is the record.