Bug 2566831 (CVE-2026-102703)

Summary: CVE-2026-102703 xen: xen: privilege escalation via improper grant copy cache validation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Xen. When processing batched grant copy operations used for memory sharing between virtual machines, the hypervisor caches internal validation data but fails to properly re-validate it when frame numbers and grant references are intermixed. A malicious guest domain can exploit this flaw by submitting crafted batch requests to bypass memory validation, potentially resulting in unauthorized host memory access, privilege escalation, or a Denial of Service (DoS).
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Bug Depends On: 2568116    
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Description OSIDB Bzimport 2026-11-04 10:44:51 UTC 
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]

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.