# CVE-2026-23057: vsock/virtio: Coalesce only linear skb

> A flaw in Linux kernel vsock/virtio allows uninitialized kernel memory disclosure when coalescing non-linear skbs in loopback transport.

- **Severity:** Not scored
- **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:** 4 Feb 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-23057, DEBIAN-CVE-2026-23057, GHSA-2725-mxxg-w826, ROOT-OS-DEBIAN-13-CVE-2026-23057, ROOT-OS-UBUNTU-2404-CVE-2026-23057, UBUNTU-CVE-2026-23057

## What is CVE-2026-23057?

CVE-2026-23057 is a vulnerability in Linux, published on 4 Feb 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:

vsock/virtio: Coalesce only linear skb

vsock/virtio common tries to coalesce buffers in rx queue: if a linear skb
(with a spare tail room) is followed by a small skb (length limited by
GOOD_COPY_LEN = 128), an attempt is made to join them.

Since the introduction of MSG_ZEROCOPY support, assumption that a small skb
will always be linear is incorrect. In the zerocopy case, data is lost and
the linear skb is appended with uninitialized kernel memory.

Of all 3 supported virtio-based transports, only loopback-transport is
affected. G2H virtio-transport rx queue operates on explicitly linear skbs;
see virtio_vsock_alloc_linear_skb() in virtio_vsock_rx_fill(). H2G
vhost-transport may allocate non-linear skbs, but only for sizes that are
not considered for coalescence; see PAGE_ALLOC_COSTLY_ORDER in
virtio_vsock_alloc_skb().

Ensure only linear skbs are coalesced. Note that skb_tailroom(last_skb) > 0
guarantees last_skb is linear.

## Which versions are affected by CVE-2026-23057?


## How do I fix CVE-2026-23057?

Apply the vendor's patch.

## Is CVE-2026-23057 being exploited?

There is no known exploitation of CVE-2026-23057 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23057 and fix it if it is affected.

What it is: CVE-2026-23057 is a vulnerability in Linux, published on 4 Feb 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-2026-23057 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-2026-23057/ (Markdown: https://insights.sbomify.com/CVE-2026-23057/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23057
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23057
- OSV: https://osv.dev/vulnerability/CVE-2026-23057

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23057/
Summaries are generated and may contain mistakes; the official description above is the record.