Bug 2550652 (CVE-2026-79611)

Summary: CVE-2026-79611 xen: xen: Denial of Service of guest virtual machines via VM entry failure
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Xen. A user inside a guest virtual machine can cause a Denial of Service (DoS) of that guest by enabling a specific combination of processor debugging and branch tracing states. Due to improper state handling during hardware virtualization transitions, the hypervisor triggers a virtual machine entry failure that unexpectedly crashes the affected guest system.
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Bug Depends On: 2559194    
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Description OSIDB Bzimport 2026-10-13 15:53:15 UTC 
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.