CVE-2013-1920 in Xen
Summary
by MITRE
Xen 4.2.x, 4.1.x, and earlier, when the hypervisor is running "under memory pressure" and the Xen Security Module (XSM) is enabled, uses the wrong ordering of operations when extending the per-domain event channel tracking table, which causes a use-after-free and allows local guest kernels to inject arbitrary events and gain privileges via unspecified vectors.
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Analysis
by VulDB Data Team • 05/06/2021
The vulnerability described in CVE-2013-1920 represents a critical flaw in the Xen hypervisor architecture that specifically manifests under memory pressure conditions when the Xen Security Module is active. This issue affects Xen versions 4.2.x, 4.1.x, and earlier releases, making it a long-standing security concern that has impacted numerous virtualized environments. The vulnerability exploits a fundamental race condition in the hypervisor's memory management and event handling mechanisms, creating a pathway for privilege escalation and arbitrary code execution within virtualized systems.
The technical root cause of this vulnerability lies in the improper ordering of operations when extending the per-domain event channel tracking table within the hypervisor's memory management subsystem. When memory pressure occurs and the XSM is enabled, the hypervisor performs a sequence of operations that fails to properly synchronize access to shared memory structures. This incorrect ordering creates a window where a local guest kernel can manipulate the event channel tracking table while it is being modified, resulting in a use-after-free condition. The flaw is particularly insidious because it leverages legitimate system operations to create an exploitable state, making detection and prevention challenging.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides local guest kernels with the ability to inject arbitrary events into the hypervisor's event processing system. This capability allows attackers to manipulate the hypervisor's internal state and potentially execute code with elevated privileges, effectively breaking the isolation guarantees that virtualization environments are designed to maintain. The vulnerability can be exploited by any local user within a guest operating system to gain unauthorized access to the host system, making it particularly dangerous in multi-tenant cloud environments where multiple users share the same physical infrastructure. The unspecified vectors of exploitation suggest that attackers can leverage various methods to trigger the vulnerability, increasing its attack surface and making it more difficult to defend against.
Mitigation strategies for this vulnerability require immediate patching of affected Xen hypervisor versions to address the flawed memory management operations and ensure proper synchronization when extending event channel tracking tables. Organizations should also implement monitoring systems to detect unusual memory pressure conditions that could trigger the vulnerability, as well as employ hypervisor hardening techniques that limit guest kernel capabilities and reduce the attack surface. The vulnerability aligns with CWE-415 which describes improper handling of memory allocation and deallocation operations, and it maps to ATT&CK technique T1055 which covers privilege escalation through kernel exploits. Additionally, this vulnerability demonstrates the importance of proper memory management in hypervisor security and the need for rigorous testing of edge cases such as memory pressure scenarios. Organizations should also consider implementing micro-segmentation and isolation techniques to limit the potential impact of such exploits, while maintaining regular security assessments to identify similar vulnerabilities in their virtualization infrastructure.