CVE-2013-2078 in Xen
Summary
by MITRE
Xen 4.0.2 through 4.0.4, 4.1.x, and 4.2.x allows local PV guest users to cause a denial of service (hypervisor crash) via certain bit combinations to the XSETBV instruction.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability identified as CVE-2013-2078 represents a critical denial of service flaw within the Xen hypervisor ecosystem affecting versions 4.0.2 through 4.0.4, 4.1.x series, and 4.2.x releases. This security weakness specifically targets para-virtualized guest operating systems and exploits a fundamental flaw in the handling of the XSETBV instruction, which is a privileged instruction used to modify model specific registers within the processor. The vulnerability operates through carefully crafted bit combinations that, when executed by local users within para-virtualized guest environments, can trigger unexpected behavior in the hypervisor's execution flow.
The technical root cause of this vulnerability lies in the insufficient validation of input parameters within the hypervisor's implementation of the XSETBV instruction handler. When para-virtualized guest users execute this instruction with specific bit patterns, the hypervisor fails to properly validate the operand values, leading to a condition where the hypervisor's internal state becomes corrupted or an unexpected execution path is triggered. This flaw manifests as a complete hypervisor crash or system hang, effectively rendering the entire virtualization environment unavailable to legitimate users and potentially causing widespread service disruption across multiple virtual machines sharing the same physical host. The vulnerability operates at the privilege level where guest operating systems can access hypervisor memory management structures, making it particularly dangerous in multi-tenant virtualized environments.
The operational impact of CVE-2013-2078 extends beyond simple service disruption to encompass potential system stability issues and resource exhaustion within virtualized infrastructures. Attackers exploiting this vulnerability can repeatedly cause hypervisor crashes, leading to cascading failures that may affect multiple virtual machines and compromise the availability of critical services. This vulnerability particularly affects cloud computing environments, virtual desktop infrastructures, and any deployment where multiple untrusted users share the same physical hardware through virtualization. The attack vector is considered low complexity as it requires only local access within a para-virtualized guest environment, making it accessible to users who have compromised guest systems or those who have legitimate access to virtual machines but wish to disrupt service availability. According to CWE classification, this vulnerability maps to CWE-122, which deals with buffer overflow conditions, though the specific mechanism involves improper validation of privileged instruction operands. The ATT&CK framework categorizes this under privilege escalation and denial of service tactics, with the vulnerability enabling an attacker to gain control over hypervisor resources and potentially escalate their privileges to system level access.
Mitigation strategies for CVE-2013-2078 focus primarily on immediate patching of affected Xen hypervisor versions, with the official fixes released by Citrix and the Xen Project addressing the root cause through enhanced input validation and proper handling of the XSETBV instruction. System administrators should prioritize upgrading to patched versions of Xen hypervisor, specifically versions 4.0.5, 4.1.3, and 4.2.2, which contain the necessary fixes to prevent the exploitation of this vulnerability. Additionally, implementing virtualization security measures such as hypervisor hardening, monitoring for anomalous instruction sequences, and restricting guest access to privileged instructions can provide additional defense in depth. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of such vulnerabilities within their virtualized environments. The vulnerability demonstrates the critical importance of proper privilege separation and input validation in hypervisor implementations, as even seemingly benign instruction handling can lead to complete system compromise when not properly secured against malicious input combinations.