# CVE-2026-99123: vsock/virtio: validate packet source for connected sockets


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111227, BELL-CVE-2026-99123, DEBIAN-CVE-2026-99123, GHSA-vf8c-hhh3-5w4x, UBUNTU-CVE-2026-99123

## What is CVE-2026-99123?

CVE-2026-99123 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

vsock/virtio: validate packet source for connected sockets

virtio_transport_recv_pkt() looks up sockets first by the full source and
destination tuple, then by destination only in the bound table. The
fallback is needed for listening and connecting sockets, but sockets remain
in the bound table after connect(), so it can also return a non-listening
socket.

The fallback does not validate the source address. In TCP_SYN_SENT, a
RESPONSE from an unrelated source can transition the victim socket to
TCP_ESTABLISHED while its stored remote address remains unchanged.
Subsequent RW packets from that source are delivered through the same
destination-only fallback.

This was reproduced with capability-empty processes under different UIDs.
The attacker discovered the target tuple through unprivileged AF_VSOCK
sock_diag and caused the victim socket to read 16 attacker-chosen bytes;
the intended peer-side socket read 0 of those 16 bytes.

Add vsock_check_source() to validate the transport, source port and source
CID against the peer stored in a non-listening socket. The local transport
is the CID exception because its packets are generated internally with
VMADDR_CID_LOCAL as their source, including connections using CID aliases.

Use the helper after lock_sock() in the virtio receive path.

## Which versions are affected by CVE-2026-99123?


## How do I fix CVE-2026-99123?

Upgrade to a fixed version.

## Is CVE-2026-99123 being exploited?

There is no known exploitation of CVE-2026-99123 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99123 and fix it if it is affected.

What it is: CVE-2026-99123 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99123 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-2026-99123/ (Markdown: https://insights.sbomify.com/CVE-2026-99123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99123
- OSV: https://osv.dev/vulnerability/CVE-2026-99123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99123/
Summaries are generated and may contain mistakes; the official description above is the record.