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CVE-2026-79611

Description

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.

Statement

This flaw is a guest-only denial of service in Xen VMX VM-entry handling (XSA-518). A user inside a guest virtual machine can crash their own guest by enabling a specific combination of processor debugging and branch tracing states; the hypervisor/host and other guest domains are unaffected.

Mitigation

Run only PV guests, or run HVM guests only on AMD/Hygon hardware (XSA-518 v2). Fixed in Fedora 44 by xen-4.21.2-4.fc44 (FEDORA-2026-839be67202).

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