# CVE-2026-31684: net: sched: act_csum: validate nested VLAN headers

> A missing bounds check in the Linux kernel's traffic control checksum action allows out-of-bounds reads and potential memory corruption when processing nested VLAN headers.

- **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:** 25 Apr 2026
- **Updated:** 1 Jun 2026
- **Also known as:** AZL-84222, BELL-CVE-2026-31684, DEBIAN-CVE-2026-31684, GHSA-gj33-f2q3-mjhg, ROOT-OS-DEBIAN-11-CVE-2026-31684, ROOT-OS-DEBIAN-12-CVE-2026-31684, ROOT-OS-UBUNTU-2204-CVE-2026-31684, ROOT-OS-UBUNTU-2404-CVE-2026-31684, UBUNTU-CVE-2026-31684

## What is CVE-2026-31684?

CVE-2026-31684 is a medium-severity memory corruption vulnerability in Linux kernel, published on 25 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:

net: sched: act_csum: validate nested VLAN headers

tcf_csum_act() walks nested VLAN headers directly from skb->data when an
skb still carries in-payload VLAN tags. The current code reads
vlan->h_vlan_encapsulated_proto and then pulls VLAN_HLEN bytes without
first ensuring that the full VLAN header is present in the linear area.

If only part of an inner VLAN header is linearized, accessing
h_vlan_encapsulated_proto reads past the linear area, and the following
skb_pull(VLAN_HLEN) may violate skb invariants.

Fix this by requiring pskb_may_pull(skb, VLAN_HLEN) before accessing and
pulling each nested VLAN header. If the header still is not fully
available, drop the packet through the existing error path.

## Which versions are affected by CVE-2026-31684?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31684?

Apply the vendor's patch.

## Is CVE-2026-31684 being exploited?

There is no known exploitation of CVE-2026-31684 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-2026-31684 and fix it if it is affected.

What it is: CVE-2026-31684 is a medium-severity memory corruption vulnerability in Linux kernel, published on 25 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-2026-31684 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-2026-31684/ (Markdown: https://insights.sbomify.com/CVE-2026-31684/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31684
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31684
- OSV: https://osv.dev/vulnerability/CVE-2026-31684

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31684/
Summaries are generated and may contain mistakes; the official description above is the record.