{"id":3968,"date":"2026-11-04T13:21:57","date_gmt":"2026-11-04T13:21:57","guid":{"rendered":"https:\/\/thedigitalfortress.us\/?p=3968"},"modified":"2026-11-04T13:21:57","modified_gmt":"2026-11-04T13:21:57","slug":"xen-hypervisor-flaws-let-one-malicious-vm-read-and-write-any-other-vms-memory","status":"publish","type":"post","link":"https:\/\/thedigitalfortress.us\/?p=3968","title":{"rendered":"Xen Hypervisor Flaws Let One Malicious VM Read and Write Any Other VM’s Memory"},"content":{"rendered":"
\n

\ue804<\/i>Swati Khandelwal<\/span>\ue802<\/i>Nov 04, 2026<\/span><\/span>Vulnerability \/ Cloud Security<\/span><\/p>\n<\/div>\n

\n
<\/a><\/div>\n

Two flaws in the Xen hypervisor allow a malicious guest virtual machine (VM) to read and write the memory of other VMs on the same host, including dom0.<\/p>\n

Dom0 is the VM that, by default, has full permissions and manages the others. Patches are out, and there is no known mitigation, the Xen Project said in an advisory<\/a> on November 3.<\/p>\n

All Xen versions from 4.6 onward are vulnerable, while 4.5 and earlier are not. The flaws are tracked as CVE-2026-102703<\/b> and CVE-2026-102704<\/b>, under Xen advisory XSA-523.<\/p>\n

The Xen Project credited AI company Anthropic <\/strong>with finding the flaws using its Claude model. Stephan Lipp of Ada Logics then validated the finding, and the CodeAnt AI Security Research Team later independently reported the same issue.<\/p>\n

The flaws are in grant copy, the operation Xen uses to copy data between VMs. Each VM tells Xen which of its memory pages other VMs may use, and Xen checks those permissions.<\/p>\n

\n
\"Cybersecurity\"<\/a><\/div>\n<\/div>\n

To save time on a batch of copies within the same memory page, Xen reuses checks it has already made. In some cases, it did not check again when it should have. That mistake is what lets a malicious guest read and write memory it does not own.<\/p>\n

<\/p>\n

XCP-ng, an open-source virtualization platform built around Xen, said in its update notes<\/a> that \u00aba single compromised guest can break out of its isolation and take over the whole host.\u00bb<\/p>\n

Xen’s advisory does not mention any attacks that exploit the flaws or specify what access within the VM an attacker needs.<\/p>\n

Qubes OS is a security-focused desktop operating system that keeps software in separate Xen-based compartments called qubes. A bulletin<\/a> said that every supported release and configuration is affected. Its fix is for Qubes 4.3, the only release it still supports<\/a>.<\/p>\n

Because every Xen version from 4.6 on is vulnerable, other products built on those versions are affected until their makers add the XSA-523 patches. As of November 4, Debian’s security tracker<\/a> listed the xen package in its bookworm, trixie, and forky releases as vulnerable, and in sid as fixed.<\/p>\n

Fixes and Restarts by Platform<\/h3>\n

These are the fixes published so far:<\/p>\n