Two vulnerabilities in the Xen hypervisor can let a malicious guest virtual machine read and write memory belonging to other VMs on the same host, including dom0, the privileged control domain. The Xen Project disclosed the flaws as CVE-2026-102703 and CVE-2026-102704 in its XSA-523 advisory.
The bugs affect grant-copy operations, which transfer memory between domains. Xen’s validation caching can mix frame numbers and grant references in one case; in the other, a check meant to restrict copying by frame number to a guest’s own memory is misplaced. Both flaws can break isolation between guest domains.
All Xen versions from 4.6 onward are affected; versions 4.5 and earlier are not. The Xen Project says no known mitigation exists. Vates lists XCP-ng 8.3 as affected and says the issue is fixed in package xen-4.17.7-4.2.xcpng8.3, documented in its security advisory.
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