CVE-2014-7155 in Xen
Summary
by MITRE
The x86_emulate function in arch/x86/x86_emulate/x86_emulate.c in Xen 4.4.x and earlier does not properly check supervisor mode permissions, which allows local HVM users to cause a denial of service (guest crash) or gain guest kernel mode privileges via vectors involving an (1) HLT, (2) LGDT, (3) LIDT, or (4) LMSW instruction.
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Analysis
by VulDB Data Team • 03/29/2022
The vulnerability identified as CVE-2014-7155 resides within the x86_emulate function in the Xen hypervisor version 4.4.x and earlier, representing a critical flaw in the virtualization layer that affects HVM (Hardware Virtual Machine) guests. This issue stems from inadequate validation of supervisor mode permissions during instruction emulation, creating a pathway for malicious exploitation that can result in either system denial of service or privilege escalation. The vulnerability specifically impacts instructions that manipulate critical system registers and control structures, including HLT (Halt), LGDT (Load Global Descriptor Table), LIDT (Load Interrupt Descriptor Table), and LMSW (Load Machine Status Word) instructions. These instructions are fundamental to system operation and require strict privilege validation to prevent unauthorized access to system resources.
The technical flaw manifests when the x86_emulate function fails to properly verify whether the executing guest kernel has sufficient privileges to perform the targeted instruction. This oversight creates a condition where local HVM users can craft malicious sequences that bypass normal privilege checks, allowing them to execute privileged operations within the guest environment. When these instructions are processed through the vulnerable emulation path, the hypervisor does not adequately validate the supervisor mode status of the requesting guest, enabling potential privilege escalation from guest kernel mode to full system control. The flaw essentially undermines the hypervisor's ability to maintain proper isolation between guest operating systems and the underlying host system, creating a direct pathway for malicious code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it enables local privilege escalation attacks that can compromise entire virtualized environments. Attackers can leverage this vulnerability to gain guest kernel mode privileges, potentially allowing them to access sensitive data, modify system configurations, or even escalate to host-level privileges depending on the virtualization setup. The denial of service aspect occurs when the malformed instruction sequences cause guest operating systems to crash or become unresponsive, disrupting service availability and potentially affecting multiple virtual machines running on the same host. This vulnerability particularly affects environments where multiple tenants share the same hypervisor infrastructure, as a compromised guest could potentially impact other guests or the host system itself.
Mitigation strategies for CVE-2014-7155 focus on upgrading to Xen versions 4.5.0 and later, where the x86_emulate function has been properly patched to enforce supervisor mode permission checks. System administrators should prioritize immediate deployment of patches and updates from Xen Project to address this vulnerability. Additional protective measures include implementing strict access controls for virtual machines, monitoring for unusual instruction sequences, and maintaining up-to-date security configurations for virtualization environments. The vulnerability aligns with CWE-284 (Improper Access Control) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) categories, reflecting the fundamental failure in access control mechanisms and privilege validation within the hypervisor layer. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and defense evasion methods, as attackers can use it to bypass normal system protections and maintain persistence within virtualized environments. Organizations should also consider implementing virtualization-specific security monitoring and incident response procedures to detect and respond to exploitation attempts targeting hypervisor vulnerabilities.