CVE-2026-31788 xen/privcmd: restrict usage in unprivileged domU
A local attacker with root access in an unprivileged Xen guest can bypass Secure Boot restrictions by modifying kernel memory via the privcmd driver.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31788?
CVE-2026-31788 is a high-severity vulnerability in Linux kernel, published on 25 Mar 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:
xen/privcmd: restrict usage in unprivileged domU
The Xen privcmd driver allows to issue arbitrary hypercalls from user space processes. This is normally no problem, as access is usually limited to root and the hypervisor will deny any hypercalls affecting other domains.
In case the guest is booted using secure boot, however, the privcmd driver would be enabling a root user process to modify e.g. kernel memory contents, thus breaking the secure boot feature.
The only known case where an unprivileged domU is really needing to use the privcmd driver is the case when it is acting as the device model for another guest. In this case all hypercalls issued via the privcmd driver will target that other guest.
Fortunately the privcmd driver can already be locked down to allow only hypercalls targeting a specific domain, but this mode can be activated from user land only today.
The target domain can be obtained from Xenstore, so when not running in dom0 restrict the privcmd driver to that target domain from the beginning, resolving the potential problem of breaking secure boot.
This is XSA-482
--- V2: - defer reading from Xenstore if Xenstore isn't ready yet (Jan Beulich) - wait in open() if target domain isn't known yet - issue message in case no target domain found (Jan Beulich)
Weakness: CWE-862
Which versions are affected by CVE-2026-31788?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31788?
Apply the vendor's patch.
Is CVE-2026-31788 being exploited?
There is no known exploitation of CVE-2026-31788 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31788, DEBIAN-CVE-2026-31788, GHSA-q397-v647-xvh6, ROOT-OS-DEBIAN-11-CVE-2026-31788, ROOT-OS-DEBIAN-12-CVE-2026-31788, ROOT-OS-DEBIAN-13-CVE-2026-31788 and 3 more.