# CVE-2026-31663: xfrm: hold dev ref until after transport_finish NF_HOOK

> A race condition in the Linux kernel's xfrm subsystem allows a use-after-free, potentially leading to code execution or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-83720, BELL-CVE-2026-31663, DEBIAN-CVE-2026-31663, GHSA-v4m9-vrgr-8xm2, ROOT-OS-DEBIAN-11-CVE-2026-31663, ROOT-OS-DEBIAN-12-CVE-2026-31663, ROOT-OS-DEBIAN-13-CVE-2026-31663, ROOT-OS-UBUNTU-2204-CVE-2026-31663, ROOT-OS-UBUNTU-2404-CVE-2026-31663, UBUNTU-CVE-2026-31663

## What is CVE-2026-31663?

CVE-2026-31663 is a high-severity use after free vulnerability in Linux kernel, published on 24 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

xfrm: hold dev ref until after transport_finish NF_HOOK

After async crypto completes, xfrm_input_resume() calls dev_put()
immediately on re-entry before the skb reaches transport_finish.
The skb->dev pointer is then used inside NF_HOOK and its okfn,
which can race with device teardown.

Remove the dev_put from the async resumption entry and instead
drop the reference after the NF_HOOK call in transport_finish,
using a saved device pointer since NF_HOOK may consume the skb.
This covers NF_DROP, NF_QUEUE and NF_STOLEN paths that skip
the okfn.

For non-transport exits (decaps, gro, drop) and secondary
async return points, release the reference inline when
async is set.

Weakness: CWE-826 (Premature Release of Resource During Expected Lifetime), CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31663?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31663?

Apply the vendor's patch.

## Is CVE-2026-31663 being exploited?

There is no known exploitation of CVE-2026-31663 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31663 and fix it if it is affected.

What it is: CVE-2026-31663 is a high-severity use after free vulnerability in Linux kernel, published on 24 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31663 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31663/ (Markdown: https://insights.sbomify.com/CVE-2026-31663/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31663
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31663
- OSV: https://osv.dev/vulnerability/CVE-2026-31663

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31663/
Summaries are generated and may contain mistakes; the official description above is the record.