VSA-2026-055: arbitrary read/write via grant copy (CVE-2026-102703, CVE-2026-102704 / XSA-523)
| Published | Updated | Severity | CVSS 4.0 | Affected products |
|---|---|---|---|---|
| 2026-11-03 | 2026-11-03 | ⚫ Critical | Not available yet | - XCP-ng 8.3 |
Two vulnerabilities in the Xen hypervisor's grant copy implementation have been discovered, allowing a malicious guest to read and write arbitrary memory, belonging to other domains, including Dom0. For Vates products, we classify the impact as Critical. For details on how we assign severity levels, see our Severity Levels Explained page.
Summary
A common access pattern is a batch of Grant Copy operations acting on adjacent address ranges in the same source or destination page. For performance reasons, Xen caches details internally to reuse already validated data. The conditions on when to re-validate the internal data were not correct in some cases:
- Frame numbers and grant references could wrongly be mixed up. This is CVE-2026-102703.
- Copying by frame number (rather than grant reference) is permitted only when operating on the caller's own memory. The check to enforce this restriction was misplaced. This is CVE-2026-102704.
Impact
A malicious guest can read and write arbitrary memory, belonging to other domains, including Dom0.
Status
- Released
Affected Versions
- XCP-ng 8.3: Affected.
Mitigation
There are no known mitigations.
Resolution
As of 2026-11-03, the xen-* packages for XCP-ng 8.3 have been updated to address these issues.
List of packages fixing this issue:
- XCP-ng 8.3:
xen-4.17.7-4.2.xcpng8.3
Credits
This issue was discovered by Anthropic using Claude, and validated by Stephan Lipp of Ada Logics. It was independently reported by the CodeAnt AI Security Research Team.