CVE-2013-4356 in Xen
Summary
by MITRE
Xen 4.3.x writes hypervisor mappings to certain shadow pagetables when live migration is performed on hosts with more than 5TB of RAM, which allows local 64-bit PV guests to read or write to invalid memory and cause a denial of service (crash).
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Analysis
by VulDB Data Team • 05/26/2021
The vulnerability identified as CVE-2013-4356 affects Xen hypervisor versions 4.3.x and represents a critical flaw in the live migration process when handling systems with substantial memory configurations. This issue specifically impacts systems with more than 5TB of RAM where the hypervisor's shadow pagetable management becomes compromised during migration operations. The vulnerability stems from improper handling of memory mappings in the hypervisor's memory management subsystem, creating a condition where guest operating systems can exploit memory access patterns to gain unauthorized access to invalid memory regions.
The technical flaw manifests when the hypervisor performs live migration of virtual machines across hosts with large memory footprints. During this process, the hypervisor writes certain hypervisor mappings to shadow pagetables, which are data structures used to track memory mappings for virtual machines. These shadow pagetables are crucial for maintaining memory isolation between the hypervisor and guest operating systems. When the memory exceeds 5TB thresholds, the hypervisor fails to properly validate or restrict these mappings, allowing 64-bit paravirtualized (PV) guest operating systems to manipulate memory references that should remain protected from guest access.
This vulnerability creates a significant operational impact as local 64-bit PV guests can leverage the flaw to either read from or write to invalid memory locations within the hypervisor's address space. The ability to access invalid memory regions provides attackers with potential pathways to escalate privileges or cause system instability. The most direct consequence is a denial of service condition that can result in hypervisor crashes, leading to complete system outages and disruption of all virtualized services running on the affected hosts. This represents a severe threat to cloud infrastructure and virtualization platforms that rely on live migration for maintenance and resource optimization.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions in memory management systems, and demonstrates characteristics consistent with the ATT&CK technique T1068, which involves local privilege escalation through kernel exploits. The flaw operates at the hypervisor level, making it particularly dangerous as it can be exploited by any local user within a paravirtualized guest environment without requiring additional privileges or network access. Organizations running Xen hypervisors in production environments with large memory configurations should prioritize immediate patching of this vulnerability, as the potential for both service disruption and security compromise makes it a critical concern for virtualization security.
Mitigation strategies should focus on implementing the official patches provided by Citrix for Xen 4.3.x versions, which address the shadow pagetable handling during live migration operations. System administrators should also consider implementing additional monitoring for unusual memory access patterns during live migration events and ensure that live migration features are disabled on systems with memory configurations exceeding the vulnerable thresholds until proper patches are applied. Network segmentation and access controls should be maintained to limit potential exploitation vectors, though the vulnerability's local nature means that physical access to the guest environment remains the primary attack surface. Regular security assessments of virtualization infrastructure should include verification of hypervisor versions and patch status to prevent similar vulnerabilities from remaining unaddressed in production environments.