Xen Hypervisor Flaws Let One Malicious VM Read and Write Any Other VM's Memory
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.
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.
Dom0 is the VM that, by default, has full permissions and manages the others, and patches are out, and there is no known mitigation, the Xen Project said in an advisory on November 3.
Stephan Lipp of Ada Logics then validated the finding, and the CodeAnt AI Security Research Team later independently reported the same issue.
XSA-523 is separate from XSA-500 , an earlier grant copy flaw that Xen disclosed on July 28, and it has its own patches.
All Xen versions from 4.6 onward are vulnerable, while 4.5 and earlier are not; qubes OS is a security-focused desktop operating system that keeps software in separate Xen-based compartments called qubes.
XCP-ng, an open-source virtualization platform built around Xen, said in its update notes that Xen's advisory does not mention any attacks that exploit the flaws or specify what access within the VM an attacker needs.
A bulletin said that every supported release and configuration is affected.
The flaws are tracked as CVE-2026-102703 and CVE-2026-102704 , under Xen advisory XSA-523; each VM tells Xen which of its memory pages other VMs may use, and Xen checks those permissions.
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.
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.
Qubes told users on November 3 to keep installing updates as normal.
What happened
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.
Dom0 is the VM that, by default, has full permissions and manages the others, and patches are out, and there is no known mitigation, the Xen Project said in an advisory on November 3.
What changed
Stephan Lipp of Ada Logics then validated the finding, and the CodeAnt AI Security Research Team later independently reported the same issue.
XSA-523 is separate from XSA-500 , an earlier grant copy flaw that Xen disclosed on July 28, and it has its own patches.
Who is affected
All Xen versions from 4.6 onward are vulnerable, while 4.5 and earlier are not; qubes OS is a security-focused desktop operating system that keeps software in separate Xen-based compartments called qubes.
Why it matters
XCP-ng, an open-source virtualization platform built around Xen, said in its update notes that Xen's advisory does not mention any attacks that exploit the flaws or specify what access within the VM an attacker needs.
A bulletin said that every supported release and configuration is affected.
Technical details
The flaws are tracked as CVE-2026-102703 and CVE-2026-102704 , under Xen advisory XSA-523; each VM tells Xen which of its memory pages other VMs may use, and Xen checks those permissions.
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.
Response
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.
What security teams should do
Qubes told users on November 3 to keep installing updates as normal.
Attribution
The Hacker News: 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.
What to watch next
Watch for revised vendor guidance, fixed versions and mitigation updates.