CVE-2017-10922 in Xen
Summary
by MITRE
The grant-table feature in Xen through 4.8.x mishandles MMIO region grant references, which allows guest OS users to cause a denial of service (loss of grant trackability), aka XSA-224 bug 3.
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Analysis
by VulDB Data Team • 12/30/2020
The CVE-2017-10922 vulnerability represents a critical flaw in the Xen hypervisor's grant-table implementation that specifically affects versions through 4.8.x. This vulnerability resides within the memory management unit handling mechanism where the hypervisor manages memory mappings between guest operating systems and the host system. The issue manifests when the grant-table feature processes MMIO region grant references, creating a scenario where legitimate memory access operations can inadvertently corrupt the grant tracking mechanism. The vulnerability is particularly concerning because it operates at the hypervisor level, affecting all virtual machines running on an affected Xen installation and potentially enabling attackers to disrupt system operations without requiring elevated privileges within individual guest environments.
The technical root cause of this vulnerability lies in the improper handling of memory mapping references within the grant-table subsystem. When guest operating systems attempt to access memory-mapped I/O regions through grant references, the hypervisor's grant tracking system fails to maintain proper reference counts and tracking information. This mismanagement results in the loss of grant trackability, where the hypervisor can no longer accurately monitor or manage the memory mappings that have been granted to guest systems. The flaw essentially creates a condition where grant references become stale or invalid, causing the hypervisor to lose track of memory regions that should remain accessible to guest operating systems. This behavior aligns with CWE-129, which describes improper handling of length parameters in memory operations, and represents a specific case of resource management failure in virtualized environments. The vulnerability operates at the intersection of hypervisor memory management and virtualization security controls, making it particularly dangerous in cloud computing and virtualization deployments.
The operational impact of CVE-2017-10922 extends beyond simple denial of service, as it fundamentally compromises the integrity of the hypervisor's memory management system. Attackers can exploit this vulnerability to cause complete loss of grant trackability, leading to potential memory corruption, guest system instability, and service disruption across all virtual machines hosted on the affected hypervisor. The vulnerability can be triggered by guest operating systems without requiring administrative privileges, making it particularly dangerous in multi-tenant environments where malicious guests could target other virtual machines on the same host. This flaw directly impacts the security posture of virtualized environments and can be classified under ATT&CK technique T1059.007 for process injection and T1499.004 for network disruption, as the vulnerability enables attackers to manipulate virtualized memory management processes. The impact is particularly severe in cloud infrastructure environments where the hypervisor manages multiple customer workloads, as a single exploited vulnerability could potentially affect numerous virtual machines simultaneously.
Mitigation strategies for CVE-2017-10922 primarily involve upgrading to patched versions of the Xen hypervisor, specifically versions 4.9.0 and later which contain the necessary fixes for grant-table handling. Organizations should implement immediate patch management procedures to ensure all affected Xen installations are updated, as the vulnerability can be exploited remotely by guest operating systems. Additional defensive measures include implementing strict memory access controls, monitoring grant table operations for unusual patterns, and conducting regular vulnerability assessments of virtualization environments. System administrators should also consider implementing network segmentation and access controls to limit the potential impact of exploitation, while maintaining detailed logging of hypervisor memory management activities to detect anomalous behavior. The vulnerability highlights the importance of proper resource tracking and memory management in virtualized environments, and organizations should review their virtualization security practices to ensure comprehensive protection against similar issues. Given the nature of hypervisor-level vulnerabilities, organizations should also consider implementing additional security controls such as hypervisor hardening, regular security audits, and continuous monitoring of virtual machine activities to prevent exploitation of similar memory management flaws.