Bug 2453800 (CVE-2026-23402)

Summary: CVE-2026-23402 kernel: KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedKeywords: Security
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) module. This vulnerability allows a host user to bypass KVM's memory management rules by overwriting critical memory structures. This can lead to a compromise of the virtual machine's memory integrity, potentially causing system instability or unexpected behavior within virtualized environments.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-01 10:02:27 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE

Adjust KVM's sanity check against overwriting a shadow-present SPTE with a
another SPTE with a different target PFN to only apply to direct MMUs,
i.e. only to MMUs without shadowed gPTEs.  While it's impossible for KVM
to overwrite a shadow-present SPTE in response to a guest write, writes
from outside the scope of KVM, e.g. from host userspace, aren't detected
by KVM's write tracking and so can break KVM's shadow paging rules.

  ------------[ cut here ]------------
  pfn != spte_to_pfn(*sptep)
  WARNING: arch/x86/kvm/mmu/mmu.c:3069 at mmu_set_spte+0x1e4/0x440 [kvm], CPU#0: vmx_ept_stale_r/872
  Modules linked in: kvm_intel kvm irqbypass
  CPU: 0 UID: 1000 PID: 872 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:mmu_set_spte+0x1e4/0x440 [kvm]
  Call Trace:
   <TASK>
   ept_page_fault+0x535/0x7f0 [kvm]
   kvm_mmu_do_page_fault+0xee/0x1f0 [kvm]
   kvm_mmu_page_fault+0x8d/0x620 [kvm]
   vmx_handle_exit+0x18c/0x5a0 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm]
   kvm_vcpu_ioctl+0x2d5/0x980 [kvm]
   __x64_sys_ioctl+0x8a/0xd0
   do_syscall_64+0xb5/0x730
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
   </TASK>
  ---[ end trace 0000000000000000 ]---
Comment 1 Mauro Matteo Cascella 2026-04-01 10:20:23 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026040110-CVE-2026-23402-c852@gregkh/T