# CVE-2026-74356: vhost: fix vhost_get_avail_idx for a non empty ring

> A logic error in the Linux kernel vhost driver causes a host livelock when mergeable buffers are enabled and the guest stalls, leading to denial of service.

- **Severity:** High 7.4 (`CVSS:3.1/AV:A/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:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-96390, BELL-CVE-2026-74356, DEBIAN-CVE-2026-74356, GHSA-pp6m-qvmq-968c, UBUNTU-CVE-2026-74356

## What is CVE-2026-74356?

CVE-2026-74356 is a high-severity denial of service vulnerability in Linux, published on 15 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:

vhost: fix vhost_get_avail_idx for a non empty ring

vhost_get_avail_idx is supposed to report whether it has updated
vq->avail_idx. Instead, it returns whether all entries have been
consumed, which is usually the same. But not always - in
drivers/vhost/net.c and when mergeable buffers have been enabled, the
driver checks whether the combined entries are big enough to store an
incoming packet. If not, the driver re-enables notifications with
available entries still in the ring. The incorrect return value from
vhost_get_avail_idx propagates through vhost_enable_notify and causes
the host to livelock if the guest is not making progress, as vhost will
immediately disable notifications and retry using the available entries.

This goes back to commit d3bb267bbdcb ("vhost: cache avail index in
vhost_enable_notify()") which changed vhost_enable_notify() to compare
the freshly read avail index against vq->last_avail_idx instead of the
previously cached vq->avail_idx. Commit 7ad472397667 ("vhost: move
smp_rmb() into vhost_get_avail_idx()") then carried over the same
comparison when refactoring vhost_enable_notify() to call the unified
vhost_get_avail_idx().

The obvious fix is to make vhost_get_avail_idx do what the comment
says it does and report whether new entries have been added.

## Which versions are affected by CVE-2026-74356?


## How do I fix CVE-2026-74356?

Apply the vendor's patch.

## Is CVE-2026-74356 being exploited?

There is no known exploitation of CVE-2026-74356 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74356 and fix it if it is affected.

What it is: CVE-2026-74356 is a high-severity denial of service vulnerability in Linux, published on 15 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-2026-74356 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-2026-74356/ (Markdown: https://insights.sbomify.com/CVE-2026-74356/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74356
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74356
- OSV: https://osv.dev/vulnerability/CVE-2026-74356

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74356/
Summaries are generated and may contain mistakes; the official description above is the record.