Executive brief
A vulnerability exists in the Xen hypervisor, which is software used to run multiple virtual machines on a single physical server. An attacker operating a guest virtual machine could exploit a flaw in how the system manages shared memory to gain unauthorized access to the host server. This could lead to a complete takeover of the physical server, theft of data from other virtual machines, or a total service outage.
Technical details
A type confusion vulnerability exists in Xen's grant-copy operations within the grant table implementation. When a grant-copy operation is initiated on a grant that is already 'pinned' by another active operation (such as a mapping or another copy), the hypervisor may fail to maintain consistency between the page used for permission checks and the page used for the actual copy operation. Specifically, the permission check may be performed on one guest frame while the copy is executed on a different one. An unprivileged guest can exploit this race-like inconsistency to bypass memory protections, leading to host privilege escalation, information disclosure, or a denial of service. The vulnerability affects Xen versions 4.2 onwards, provided CONFIG_GRANT_TABLE is enabled. Patches are available for stable branches including 4.17.x and 4.18.x.
Affected products
- Xen Project Xen 4.2 through 4.18.x
Timeline
- 2026-07-28: disclosed
- 2026-07-28: advisory
- 2026-07-28: patched