CVE-2026-31788

Summary

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)

Affected Software

VendorProductVersion RangeStatus
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 4eb245ff0d33b618e097a2c23de5df56d4ad6969affected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 3ee5b9e3de4b8bdd74183d83205481c91a9effc8affected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 87a803edb2ded911cb587c53bff179d2a2ed2a28affected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 1879319d790f7d57622cdc22807b60ea78b56b6daffected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 78432d8f0372c71c518096395537fa12be7ff24eaffected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 389bae9a4409934e8b8d4dbdaaf02a3ae71cf8e4affected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < cbede2e833da1893afbea9b3ff29b5dda23a4a91affected
LinuxLinux1c5de1939c204bde9cce87f4eb3d26e9f9eb732b < 453b8fb68f3641fea970db88b7d9a153ed2a37e8affected
LinuxLinux2.6.37affected
LinuxLinux0 < 2.6.37unaffected
LinuxLinux5.10.253 <= 5.10.*unaffected
LinuxLinux5.15.203 <= 5.15.*unaffected
LinuxLinux6.1.167 <= 6.1.*unaffected
LinuxLinux6.6.130 <= 6.6.*unaffected
LinuxLinux6.12.78 <= 6.12.*unaffected
LinuxLinux6.18.20 <= 6.18.*unaffected
LinuxLinux6.19.10 <= 6.19.*unaffected
LinuxLinux7.0 <= *unaffected

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

References