CVE-2016-2271 in Xen
Summary
by MITRE
VMX in Xen 4.6.x and earlier, when using an Intel or Cyrix CPU, allows local HVM guest users to cause a denial of service (guest crash) via vectors related to a non-canonical RIP.
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Analysis
by VulDB Data Team • 08/23/2018
The vulnerability identified as CVE-2016-2271 represents a critical denial of service flaw within the Xen hypervisor version 4.6.x and earlier releases. This issue specifically affects systems utilizing Intel or Cyrix processors in hardware virtualization mode, where the Virtual Machine Extensions (VMX) functionality is enabled. The vulnerability manifests when local users within a Hardware Virtual Machine (HVM) guest environment attempt to manipulate certain processor states, leading to unexpected system behavior that ultimately results in guest crash conditions.
The technical root cause of this vulnerability lies within the hypervisor's handling of non-canonical return instruction pointers (RIP) during virtualized execution contexts. When a guest operating system executes code that generates a non-canonical RIP value, the Xen hypervisor fails to properly validate or handle this condition, allowing malicious guest users to craft specific instruction sequences that trigger the hypervisor to crash. This represents a flaw in the processor state management mechanism within the VMX implementation, where the hypervisor does not adequately protect against malformed instruction pointer values that could originate from guest execution contexts.
The operational impact of CVE-2016-2271 extends beyond simple service disruption, as it enables local privilege escalation within virtualized environments where users might not normally have access to critical system resources. While the vulnerability primarily results in guest crashes rather than direct system compromise, it can be leveraged as part of broader attack strategies to disrupt virtualized services or as a stepping stone for more sophisticated attacks. The vulnerability affects all systems running Xen hypervisors version 4.6.x and earlier, making it particularly concerning for organizations maintaining older virtualization infrastructure.
This vulnerability aligns with CWE-122, which addresses improper restriction of operations within a recognized security boundary, and demonstrates weaknesses in privilege separation and memory management within virtualization contexts. From an attack perspective, it maps to ATT&CK technique T1059.001 for command and scripting interpreter execution, as attackers can manipulate guest environments to trigger the vulnerability. The issue also connects to T1499.004 for network denial of service, as the guest crash can effectively disrupt service availability within virtualized environments. Organizations should prioritize immediate patching of affected Xen installations to prevent exploitation, as the vulnerability can be triggered through normal guest execution without requiring special privileges beyond those normally available to guest users.
The remediation strategy involves upgrading to Xen hypervisor versions 4.7.0 and later, where the VMX handling has been properly addressed. System administrators should also implement monitoring solutions to detect unusual guest crash patterns that might indicate exploitation attempts. Additionally, organizations should review their virtualization security policies to ensure proper isolation between guest environments and implement network segmentation to limit potential impact from successful exploitation attempts.