CVE-2013-1432 in Xen
Summary
by MITRE
Xen 4.1.x and 4.2.x, when the XSA-45 patch is in place, does not properly maintain references on pages stored for deferred cleanup, which allows local PV guest kernels to cause a denial of service (premature page free and hypervisor crash) or possible gain privileges via unspecified vectors.
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Analysis
by VulDB Data Team • 05/17/2021
The vulnerability identified as CVE-2013-1432 represents a critical flaw in the Xen hypervisor version 4.1.x and 4.2.x series that manifests when the XSA-45 security patch is implemented. This issue stems from improper reference management within the hypervisor's memory management subsystem, specifically affecting pages designated for deferred cleanup operations. The flaw exists in the interaction between the hypervisor's memory management and the privilege separation mechanisms that govern how virtual machines interact with the underlying hardware resources.
The technical root cause of this vulnerability lies in the hypervisor's failure to properly maintain reference counts on memory pages that are scheduled for deferred cleanup. When the XSA-45 patch is active, the system maintains a queue of pages that require cleanup but cannot be immediately freed due to pending operations or references. The flaw occurs when the hypervisor incorrectly processes these references, leading to premature page deallocation. This improper reference handling creates a scenario where local privileged virtual machine kernels can manipulate the reference counting mechanisms to either force the premature freeing of memory pages or cause the hypervisor to crash during cleanup operations.
From an operational perspective, this vulnerability presents a significant risk to virtualized environments as it allows local privilege escalation within the guest operating system to potentially affect the entire hypervisor infrastructure. The impact ranges from denial of service conditions that can crash the hypervisor and terminate all running virtual machines to more severe privilege escalation scenarios where guest kernels might gain unauthorized access to hypervisor-level resources. The vulnerability is particularly concerning because it operates within the hypervisor's memory management layer, which is fundamental to the security isolation between virtual machines and the host system.
The attack surface for this vulnerability is primarily limited to local users within privileged virtual machine environments, but the potential consequences are severe enough to warrant immediate attention. The flaw demonstrates a classic memory management issue that aligns with CWE-129, which deals with improper handling of reference counts and resource management. This vulnerability also maps to several ATT&CK techniques including privilege escalation through kernel exploits and denial of service attacks against critical system components. The issue represents a failure in the hypervisor's memory management subsystem to properly enforce reference counting semantics, creating a pathway for malicious code to exploit the underlying resource management mechanisms.
Organizations should prioritize applying the appropriate security patches from Xen project releases that address the reference counting issues in the deferred cleanup mechanism. The recommended mitigation strategy involves upgrading to Xen versions that contain fixes for this specific reference management flaw, along with implementing monitoring systems to detect potential exploitation attempts. Security teams should also consider implementing additional isolation measures and regularly auditing virtual machine memory usage patterns to identify anomalous behavior that might indicate exploitation attempts. The vulnerability highlights the critical importance of proper resource management in hypervisor environments and underscores the need for comprehensive testing of security patches before deployment in production systems.