Xen Hypervisor VMX VMEntry Failure (CVE-2026-79611)
CVE-2026-79611 Published on October 13, 2026

VMX: VMentry failure with branch tracing and blocked states
For XSA-308 logic was introduced, as VMX VMEntry checks do not like the exact combination of state which occurs when #DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is fatal to the guest. Sadly there is another special sub-case of the above, with branch tracing enabled. In that case the prior adjustment would still cause a VMentry failure, as before fatal to the guest.