CVE-2014-7156 in Xen
Summary
by MITRE
The x86_emulate function in arch/x86/x86_emulate/x86_emulate.c in Xen 3.3.x through 4.4.x does not check the supervisor mode permissions for instructions that generate software interrupts, which allows local HVM guest users to cause a denial of service (guest crash) via unspecified vectors.
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Analysis
by VulDB Data Team • 03/29/2022
The vulnerability identified as CVE-2014-7156 resides within the x86_emulate function in the Xen hypervisor's architecture layer, specifically in the file arch/x86/x86_emulate/x86_emulate.c. This flaw affects Xen versions 3.3.x through 4.4.x and represents a critical security oversight in the handling of supervisor mode permissions for software interrupt instructions. The vulnerability stems from insufficient validation mechanisms that fail to properly enforce privilege checks when processing certain x86 instructions that generate software interrupts. This weakness allows malicious users within HVM (Hardware Virtual Machine) guest environments to exploit the hypervisor's instruction emulation logic and potentially cause system instability.
The technical flaw manifests when the x86_emulate function processes instructions that generate software interrupts without verifying whether the executing context has appropriate supervisor mode permissions. This failure creates a privilege escalation vector where unprivileged guest users can manipulate the hypervisor's execution flow through carefully crafted instruction sequences. The absence of proper permission checking for supervisor mode operations means that guest users can bypass normal access controls and execute instructions that should only be available to the hypervisor itself or privileged kernel components. This vulnerability specifically targets the hypervisor's emulation layer, which is responsible for translating and executing x86 instructions that cannot be directly handled by the physical processor.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise the integrity of virtualized environments. Local users within HVM guest operating systems can exploit this weakness to cause guest crashes, effectively creating a denial of service condition that affects the availability of virtualized applications and services. The instability introduced by this vulnerability can lead to complete system crashes, requiring manual intervention to restore normal operations. Additionally, the vulnerability may serve as a stepping stone for more sophisticated attacks, as it demonstrates a fundamental flaw in the hypervisor's privilege enforcement mechanisms that could potentially be leveraged to escalate privileges or gain unauthorized access to other virtual machines or the host system itself.
Mitigation strategies for CVE-2014-7156 require immediate patching of affected Xen hypervisor versions, with administrators prioritizing updates to versions 4.5.x or later where the vulnerability has been addressed. System administrators should implement comprehensive monitoring of virtualized environments to detect potential exploitation attempts and establish robust incident response procedures. The vulnerability aligns with CWE-284, which addresses improper privilege management, and maps to ATT&CK technique T1068, involving local privilege escalation through improper access control. Organizations should also consider implementing additional security controls such as virtual machine isolation measures, regular security assessments of virtualized environments, and maintaining up-to-date security patches across all hypervisor components. The remediation process must include thorough testing of patched systems to ensure that the vulnerability fix does not introduce compatibility issues with existing virtualized applications or services.