CVE-2026-31788
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)
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Linux privcmd driver in Xen guests could bypass kernel lockdown (secure boot) by issuing arbitrary hypercalls; now restricted to a specific target domain.
Vulnerability
The Linux kernel's privcmd driver, used in Xen virtual machines, allows userspace processes to issue arbitrary hypercalls. While normally restricted to root and blocked by the hypervisor for cross-domain operations, the driver can be abused to circumvent kernel lockdown (secure boot) in unprivileged domains. By modifying page tables, a root user can enable user-mode access to kernel memory, breaking secure boot guarantees [1][4].
Exploitation
An attacker requires root privileges within a PV, PVH, or HVM guest booted with secure boot. The privcmd driver does not restrict hypercalls to the intended target domain by default, allowing manipulation of kernel memory. The only legitimate use case for an unprivileged domU is when it acts as a device model for another guest, but the driver lacked built-in enforcement [2][3].
Impact
Successful exploitation allows a privileged user in a secure-booted guest to perform actions that compromise kernel integrity, defeating the purpose of secure boot. This undermines the trust model of a secure Xen deployment [1][4].
Mitigation
Patches (xsa482-linux-1.patch and xsa482-linux-2.patch) have been released by the Linux kernel and Xen project. They restrict privcmd to only accept hypercalls targeting the domain obtained from Xenstore when not running in dom0. Users must apply these patches to their guest kernels; no workarounds are available [1][4].
AI Insight generated on May 18, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
10cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*+ 9 more
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*range: >=2.6.37.1,<5.10.253
- cpe:2.3:o:linux:linux_kernel:2.6.37:-:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*
- (no CPE)
Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
14- xenbits.xen.org/xsa/advisory-482.htmlnvdPatchThird Party Advisory
- git.kernel.org/stable/c/1879319d790f7d57622cdc22807b60ea78b56b6dnvdPatch
- git.kernel.org/stable/c/389bae9a4409934e8b8d4dbdaaf02a3ae71cf8e4nvdPatch
- git.kernel.org/stable/c/3ee5b9e3de4b8bdd74183d83205481c91a9effc8nvdPatch
- git.kernel.org/stable/c/453b8fb68f3641fea970db88b7d9a153ed2a37e8nvdPatch
- git.kernel.org/stable/c/4eb245ff0d33b618e097a2c23de5df56d4ad6969nvdPatch
- git.kernel.org/stable/c/78432d8f0372c71c518096395537fa12be7ff24envdPatch
- git.kernel.org/stable/c/87a803edb2ded911cb587c53bff179d2a2ed2a28nvdPatch
- git.kernel.org/stable/c/cbede2e833da1893afbea9b3ff29b5dda23a4a91nvdPatch
- www.openwall.com/lists/oss-security/2026/03/24/2nvdMailing List
- www.openwall.com/lists/oss-security/2026/03/24/3nvdMailing List
- www.openwall.com/lists/oss-security/2026/03/24/4nvdMailing List
- www.openwall.com/lists/oss-security/2026/03/24/5nvdMailing List
- www.openwall.com/lists/oss-security/2026/03/26/4nvdMailing List
News mentions
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