CVE-2013-4553 in Xen
Summary
by MITRE
The XEN_DOMCTL_getmemlist hypercall in Xen 3.4.x through 4.3.x (possibly 4.3.1) does not always obtain the page_alloc_lock and mm_rwlock in the same order, which allows local guest administrators to cause a denial of service (host deadlock).
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Analysis
by VulDB Data Team • 06/02/2021
The vulnerability identified as CVE-2013-4553 affects the Xen hypervisor version 3.4.x through 4.3.x, potentially including version 4.3.1, and represents a critical concurrency issue within the memory management subsystem. This flaw specifically resides in the XEN_DOMCTL_getmemlist hypercall implementation, which is responsible for retrieving memory allocation information from guest domains. The vulnerability stems from improper locking mechanisms that fail to maintain consistent lock ordering across different execution paths within the hypervisor's memory management code.
The technical root cause of this vulnerability lies in the inconsistent acquisition of two critical kernel locks: page_alloc_lock and mm_rwlock. When processing the getmemlist hypercall, the hypervisor code does not always acquire these locks in the same predetermined order, creating a potential deadlock scenario. This lock ordering violation occurs because the code path for handling memory list requests may acquire locks in different sequences depending on execution conditions, guest memory state, or specific memory allocation patterns. The inconsistency in lock acquisition order creates a classic deadlock condition where one thread holds a lock while waiting for another, which is held by a second thread that in turn waits for the first lock, resulting in a complete system hang.
Local guest administrators can exploit this vulnerability by carefully crafting memory allocation patterns and hypercall sequences that trigger the specific lock ordering scenario. The attack requires the attacker to have administrative privileges within a guest operating system, but does not require root access or special privileges beyond what is typically available to domain administrators. The exploitation results in a denial of service condition that affects the entire host system, causing a complete deadlock that prevents any further virtual machine operations or host management activities. This makes the vulnerability particularly dangerous in multi-tenant environments where guest administrators might intentionally or unintentionally trigger the condition.
The operational impact of this vulnerability extends beyond simple service disruption to create potential security implications for cloud environments and virtualized infrastructures. When a host system becomes deadlocked due to this vulnerability, all virtual machines running on that host become unresponsive, effectively creating a denial of service for all users of that infrastructure. The vulnerability affects the fundamental stability of virtualized environments, making it a critical concern for organizations relying on Xen hypervisors for their virtualization needs. The issue is particularly concerning in cloud computing scenarios where multiple customers share the same physical infrastructure, as a single malicious guest could potentially disrupt services for all other virtual machines on the same host.
This vulnerability maps directly to CWE-362, which describes Concurrent Execution using Shared Resource with Improper Synchronization, and represents a classic case of improper locking sequence that violates fundamental concurrency control principles. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, as it allows local administrators to achieve a system-wide impact through carefully crafted memory management operations. The vulnerability demonstrates how seemingly minor implementation details in kernel code can create catastrophic system-wide failures, highlighting the importance of rigorous lock ordering validation in hypervisor implementations. Organizations should implement immediate mitigation strategies including upgrading to patched versions of Xen hypervisor, implementing monitoring for unusual memory allocation patterns, and establishing proper access controls to limit guest administrative privileges where possible.
The remediation approach requires upgrading to Xen versions that have addressed the lock ordering issue through proper synchronization mechanisms. Security patches typically involve ensuring consistent lock acquisition order throughout all code paths that access shared memory management resources. Additionally, organizations should conduct thorough testing of hypervisor upgrades in staging environments before deployment to ensure compatibility with existing virtual machine configurations. Regular security assessments of virtualization environments should include checks for similar concurrency issues, particularly in hypervisor code that handles memory management operations. The vulnerability serves as a reminder of the critical importance of proper synchronization mechanisms in hypervisor implementations, as even local privilege escalation can result in system-wide denial of service conditions that compromise entire virtualized infrastructures.