CVE-2026-79610
Description
A flaw was found in Xen. When a guest virtual machine repeatedly changes grant table configurations, the hypervisor frees and reallocates status memory pages, rendering previously calculated pointers invalid. A malicious guest can exploit these stale pointers to corrupt hypervisor memory, potentially leading to host privilege escalation or a Denial of Service (DoS) condition.
Statement
A flaw was found in Xen's grant table handling. A guest repeatedly switching grant table versions (v2→v1→v2) causes status pages to be freed and reallocated, leaving stale pointers that a malicious guest can use to corrupt hypervisor memory, leading to host privilege escalation, information leaks, or DoS. Xen 4.0 onwards is vulnerable (3.4 and earlier not); preconditions: x86 guests permitted grant table v2, multi-vCPU guests only. Fedora's xen 4.20.4 is in the vulnerable range; no fixed release is available yet (XSA-517 patch pending).
Mitigation
Set gnttab=max-ver:1 on the hypervisor command line, or max_grant_version=1 in the guest configuration, to prevent use of grant table v2.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the expired pointer is used in a read operation, an attacker might be able to control data read in by the application.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the expired pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" (such as NULL) or larger than expected by a read or write operation, then a crash may occur.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If the expired pointer is used in a function call, or points to unexpected data in a write operation, then code execution may be possible.
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