# CVE-2026-74684: net: tap: set skb->dev before parsing virtio net header in tap_get_user_xdp()

> A missing device assignment in the Linux kernel's TAP driver causes a null pointer dereference and system crash when processing specific XDP buffers.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-97242, BELL-CVE-2026-74684, DEBIAN-CVE-2026-74684, GHSA-23q4-679m-qgxw, UBUNTU-CVE-2026-74684

## What is CVE-2026-74684?

CVE-2026-74684 is a high-severity vulnerability in Linux, published on 22 Aug 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: tap: set skb->dev before parsing virtio net header in tap_get_user_xdp()

The commit 4f61f133f354 ("net: tap: NULL pointer derefence in
dev_parse_header_protocol when skb->dev is null") fixed a crash in
tap_get_user() by assigning skb->dev before calling tun_vnet_hdr_to_skb().
This is required because virtio_net_hdr_to_skb() may invoke
dev_parse_header_protocol(), which dereferences skb->dev. Without the
assignment, a NULL pointer dereference can occur.

However, tap_get_user_xdp() still parses the virtio-net header before
assigning skb->dev. When the vhost TX path passes an XDP buffer containing
a GSO virtio-net header but the protocol is set to zero on purpose,
tun_vnet_hdr_to_skb() can reach dev_parse_header_protocol() while skb->dev
is still NULL, resulting in a crash.

Fix this by looking up the tap device and assigning skb->dev before calling
tun_vnet_hdr_to_skb(), matching the ordering already used in
tap_get_user(). Preserve the existing RCU read-side critical section across
dev_queue_xmit().

## Which versions are affected by CVE-2026-74684?


## How do I fix CVE-2026-74684?

Apply the vendor's patch.

## Is CVE-2026-74684 being exploited?

There is no known exploitation of CVE-2026-74684 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74684 and fix it if it is affected.

What it is: CVE-2026-74684 is a high-severity vulnerability in Linux, published on 22 Aug 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-2026-74684 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-2026-74684/ (Markdown: https://insights.sbomify.com/CVE-2026-74684/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74684
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74684
- OSV: https://osv.dev/vulnerability/CVE-2026-74684

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74684/
Summaries are generated and may contain mistakes; the official description above is the record.