# CVE-2026-31664: xfrm: clear trailing padding in build_polexpire()

> Uninitialized kernel heap memory is leaked to userspace via netlink multicast in the Linux kernel's XFRM subsystem.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 15 Oct 2026
- **Also known as:** AZL-83873, BELL-CVE-2026-31664, DEBIAN-CVE-2026-31664, GHSA-5fvv-6wpc-9mr7, ROOT-OS-DEBIAN-11-CVE-2026-31664, ROOT-OS-DEBIAN-12-CVE-2026-31664, ROOT-OS-UBUNTU-2204-CVE-2026-31664, ROOT-OS-UBUNTU-2404-CVE-2026-31664, UBUNTU-CVE-2026-31664

## What is CVE-2026-31664?

CVE-2026-31664 is a medium-severity 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: clear trailing padding in build_polexpire()

build_expire() clears the trailing padding bytes of struct
xfrm_user_expire after setting the hard field via memset_after(),
but the analogous function build_polexpire() does not do this for
struct xfrm_user_polexpire.

The padding bytes after the __u8 hard field are left
uninitialized from the heap allocation, and are then sent to
userspace via netlink multicast to XFRMNLGRP_EXPIRE listeners,
leaking kernel heap memory contents.

Add the missing memset_after() call, matching build_expire().

## Which versions are affected by CVE-2026-31664?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31664?

Apply the vendor's patch.

## Is CVE-2026-31664 being exploited?

There is no known exploitation of CVE-2026-31664 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-2026-31664 and fix it if it is affected.

What it is: CVE-2026-31664 is a medium-severity 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-2026-31664 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-2026-31664/ (Markdown: https://insights.sbomify.com/CVE-2026-31664/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31664
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31664
- OSV: https://osv.dev/vulnerability/CVE-2026-31664

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31664/
Summaries are generated and may contain mistakes; the official description above is the record.