CVE-2026-27211 is a critical (CVSS 10.0) flaw in Cloud Hypervisor versions 34.0 through 50.0. A malicious guest can make virtio-block raw images serve host file contents back to it, within the process privileges. Version 50.1 fixes it. Upgrade, and enable Landlock sandboxing as a workaround.
What's affected
Cloud Hypervisor 34.0 through 50.0, when using virtio-block devices backed by raw images. The attack needs the backing image to be writable by the guest or to come from an untrusted source. Deployments using only trusted, read only images are not affected.
The fix is in 50.1, and the project also lists release 51.0.
How to check if you're exposed
cloud-hypervisor --version
Then review your disk configuration. Look for raw images that guests can write to, or that came from users or third parties. Those match the preconditions in the advisory.
What to do now
- Upgrade Cloud Hypervisor to 50.1 or later.
- Use read only images where guests do not need to write to the disk.
- Enable Landlock sandboxing and restrict the privileges and file access of the process, which is the workaround the record gives.
- Specify the image format explicitly instead of relying on auto detection where your tooling allows it.
- Review guests that write to raw disks and consider them untrusted.
Why it matters
The record lists CWE-73, external control of file name or path. The hypervisor guessed the image format from the disk header. A guest that can write its own header can make the host treat the disk as a different format that points at a file on the host.
Guest to host boundaries are the core promise of virtualization. Format auto detection on guest controlled data weakens that promise, so the fix and the workaround both limit what the process can reach. The record does not mark this CVE as known exploited.
Quick check
Who is not affected?
Deployments that use only trusted, read only images, according to the record.
Sources
- CVE-2026-27211 on Gold
- Release listed in the record: https://github.com/cloud-hypervisor/cloud-hypervisor/releases/tag/v50.1
- Release listed in the record: https://github.com/cloud-hypervisor/cloud-hypervisor/releases/tag/v51.0
Last reviewed: 19 October 2026.
