CVE-2026-62435 in Xen
Summary
by MITRE • 07/28/2026
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]
With the introduction of Grant Table v2 came the requirement to be able to switch between versions. Switching from v1 to v2 reduces the number of valid grant references, as a bigger shared entry structure is then needed while the shared table doesn't change size. Switching from v2 back to v1 the status frames, which are separate in v2, go away.
Code holding, but intermediately dropping and then re-acquiring the grant table lock, sometimes wrongly assumes that said properties wouldn't change across the window in time where the lock is not being held.
The v1 -> v2 issue is CVE-2026-62435.
The v2 -> v1 issue is CVE-2026-62436.
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Analysis
by VulDB Data Team • 07/28/2026
The vulnerability described represents a critical race condition in Xen hypervisor grant table management that spans across two distinct CVE identifiers, highlighting the complexity of virtualization security controls. This flaw manifests in the transition mechanisms between different grant table versions, specifically affecting how the hypervisor handles memory sharing and reference tracking during version switching operations. The underlying issue stems from improper assumptions about the stability of grant table properties during temporary lock release periods, creating potential attack vectors that could be exploited to manipulate memory access permissions or bypass security controls.
The technical implementation of grant tables in Xen hypervisors requires careful management of shared memory references between guest operating systems and the host system. When transitioning from version 1 to version 2 of the grant table structure, the system must adjust its handling of reference counts and shared entry structures while maintaining compatibility with existing memory mappings. The v1 to v2 transition specifically identified as CVE-2026-62435 suffers from code that temporarily releases the grant table lock but fails to account for potential changes in reference validity during this window, creating opportunities for inconsistent state management. This vulnerability directly relates to CWE-362, which describes race conditions where concurrent access to shared resources results in unpredictable behavior.
The operational impact of CVE-2026-62435 extends beyond simple memory corruption scenarios, potentially enabling privilege escalation attacks or information disclosure through manipulation of grant table references during version transitions. An attacker could exploit this vulnerability by forcing the hypervisor to switch between grant table versions while simultaneously attempting to access shared memory regions, leading to potential data leakage or unauthorized memory access patterns. The flaw essentially creates a temporal inconsistency in the hypervisor's memory management logic where assumptions about reference stability prove incorrect during lock release windows.
The reverse transition from v2 back to v1, identified as CVE-2026-62436, presents an equally serious concern with different operational characteristics but comparable security implications. This issue affects how the hypervisor manages status frames that are separated in version 2 but consolidated in version 1, creating potential for memory management inconsistencies and reference corruption. When the grant table lock is released during this transition process, the system assumes that previously valid references remain valid even though the underlying structure has fundamentally changed, leading to potential dereference of invalid memory addresses or incorrect access control enforcement.
Both vulnerabilities collectively represent a failure in hypervisor-level memory management that could be leveraged through techniques aligned with ATT&CK tactic T1059 for privilege escalation and T1566 for initial compromise. The race condition aspects of these flaws make them particularly dangerous as they can be triggered through normal system operations without requiring special privileges, potentially allowing attackers to manipulate hypervisor state during legitimate memory management operations. The fundamental issue lies in the hypervisor's assumption that shared data structures remain consistent across temporary lock release periods, a common pattern in concurrent programming that has been properly addressed in other security contexts but failed in this specific implementation.
Mitigation strategies for these vulnerabilities must address both the immediate code-level fixes required to ensure proper lock handling during grant table transitions and broader architectural improvements to prevent similar race conditions in hypervisor memory management systems. System administrators should implement immediate patches that enforce proper locking mechanisms and validate reference consistency across version transitions, while also monitoring for potential exploitation attempts through abnormal grant table access patterns. The remediation process must include comprehensive testing of grant table transition paths to ensure that no other race conditions exist within the hypervisor's memory management subsystems, as these vulnerabilities could indicate broader architectural weaknesses in concurrent access controls that require additional security hardening measures.