Xen Hypervisor Flaws Let One Malicious VM Read and Write Any Other VM's Memory

Two critical vulnerabilities in the Xen hypervisor, tracked as CVE-2026-102703 and CVE-2026-102704, allow a malicious guest virtual machine to read and write memory from other VMs on the same host, including the privileged dom0. The flaws reside in the grant copy mechanism used for inter-VM memory operations, where permission checks are incorrectly reused, breaking VM isolation. All Xen versions from 4.6 onward are affected, with no known mitigations other than patching. The vulnerabilities impact downstream projects like XCP-ng and Qubes OS, which have released updates to address the issues.

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