In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Bail from shadow walks if the root is invalid or a dummy When… (CVE-2026-98717)

The vulnerability in the Linux kernel KVM x86 MMU involved improper handling of shadow page table walks when the root was a dummy root backed by the zero page. If a race condition occurred between memslot creation and a stage-2 page fault, KVM could attempt to walk shadow page tables using the zero page, resulting in a NULL pointer dereference and kernel oops. The patch ensures that shadow walks bail out immediately if the root is invalid or dummy, preventing the NULL dereference. Additional hardening was added to warn on fully invalid roots, although dummy roots do not trigger warnings as they are expected to be valid enough to allow guest entry.

This vulnerability can cause a kernel NULL pointer dereference leading to a kernel oops and potential denial of service in virtualized environments using KVM. The impact is limited to kernel stability and does not indicate privilege escalation or data corruption. No known exploits in the wild have been reported.

A fix has been implemented in the Linux kernel to terminate shadow page table walks when encountering dummy or invalid roots, preventing NULL pointer dereferences. Users should update to the fixed kernel version once available. Patch status is not explicitly confirmed in the provided data; check the vendor advisory for current remediation guidance.