Search: CVE-2025-21839

CVE-2025-21839 is a vulnerability in the Linux kernel's KVM x86 virtualization subsystem involving improper handling of the debug register DR6. The issue arises from loading the guest's DR6 value inside the core vcpu_run() loop, which can cause stale values to be loaded into hardware, particularly affecting nested virtualization scenarios. This can lead to incorrect DR6 values being observed by the guest, potentially causing instability or denial of service. The vulnerability has been fixed by moving the loading of DR6 with the guest value to before entering the vcpu_run() loop.