# CVE-2026-74742: veth: fix queue index used to wake the peer txq in veth_poll

> A logic error in the Linux kernel veth driver causes network queue stalls in multi-queue setups without XDP, leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 26 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** BELL-CVE-2026-74742, DEBIAN-CVE-2026-74742, GHSA-pp8f-5mj5-qp78, UBUNTU-CVE-2026-74742

## What is CVE-2026-74742?

CVE-2026-74742 is a high-severity denial of service vulnerability in Linux, published on 26 Aug 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:

veth: fix queue index used to wake the peer txq in veth_poll

veth_poll() derives the index of the peer TX queue to wake from
rq->xdp_rxq.queue_index. That field is only initialized by
xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an
XDP program is attached. On the plain GRO/NAPI path
(veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so
queue_index stays 0 for every queue, as priv->rq is zero-allocated.

So in a multi-queue setup with GRO enabled and no XDP program attached,
every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops
peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing
ever wakes it again: the poller draining queue 1 wakes queue 0 instead.
veth implements no ndo_tx_timeout, so the netdev watchdog does not kick
in either, and the queue stays stopped indefinitely.

Derive the index from the position of the rq within priv->rq instead,
which is correct regardless of whether XDP was ever enabled.

Scripts to reproduce the stall are available at
https://github.com/netoptimizer/veth-backpressure-performance-testing

## Which versions are affected by CVE-2026-74742?


## How do I fix CVE-2026-74742?

Apply the vendor's patch.

## Is CVE-2026-74742 being exploited?

There is no known exploitation of CVE-2026-74742 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74742 and fix it if it is affected.

What it is: CVE-2026-74742 is a high-severity denial of service vulnerability in Linux, published on 26 Aug 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-2026-74742 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-2026-74742/ (Markdown: https://insights.sbomify.com/CVE-2026-74742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74742
- OSV: https://osv.dev/vulnerability/CVE-2026-74742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74742/
Summaries are generated and may contain mistakes; the official description above is the record.