CVE-2014-8595 in Xen
Summary
by MITRE
arch/x86/x86_emulate/x86_emulate.c in Xen 3.2.1 through 4.4.x does not properly check privileges, which allows local HVM guest users to gain privileges or cause a denial of service (crash) via a crafted (1) CALL, (2) JMP, (3) RETF, (4) LCALL, (5) LJMP, or (6) LRET far branch instruction.
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Analysis
by VulDB Data Team • 02/25/2022
The vulnerability identified as CVE-2014-8595 resides within the x86 emulation subsystem of the Xen hypervisor, specifically in the arch/x86/x86_emulate/x86_emulate.c file. This flaw affects Xen versions ranging from 3.2.1 through 4.4.x, representing a significant security gap that impacts virtualized environments where HVM (Hardware Virtual Machine) guests operate. The vulnerability stems from insufficient privilege validation during the processing of far branch instructions, which are critical control flow operations that can transfer execution to different code segments with potentially different privilege levels.
The technical implementation of this vulnerability involves the improper handling of privilege checks when processing six specific far branch instructions: CALL, JMP, RETF, LCALL, LJMP, and LRET. These instructions are fundamental to x86 architecture and are commonly used for function calls, jumps, and return operations across different code segments. When a local user within an HVM guest system executes one of these crafted instructions, the hypervisor fails to properly validate whether the operation should be permitted based on the current privilege level and segment descriptor attributes. This oversight creates a potential privilege escalation pathway where unprivileged guest users can manipulate the hypervisor's execution flow to gain elevated privileges or force system crashes.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it also enables denial of service conditions that can crash the entire hypervisor system. This dual nature makes the vulnerability particularly dangerous in production environments where system stability and security are paramount. Attackers can leverage this flaw to either elevate their privileges within the guest environment to gain access to sensitive data or system resources, or to cause a complete system crash that results in service disruption. The vulnerability affects all HVM guest configurations and poses a significant risk to cloud infrastructure, virtualized servers, and any system relying on Xen hypervisor for virtualization services.
Mitigation strategies for CVE-2014-8595 require immediate patching of affected Xen hypervisor versions to the latest stable releases that contain the necessary privilege checking fixes. Organizations should also implement monitoring for suspicious far branch instruction usage patterns within their virtualized environments and consider isolating critical systems from potentially compromised guest environments. The vulnerability aligns with CWE-284 (Improper Access Control) and can be categorized under ATT&CK technique T1068 (Local Privilege Escalation) and T1499 (Endpoint Denial of Service). System administrators should prioritize updating their Xen installations and conducting thorough security assessments of their virtualized infrastructure to prevent exploitation of this privilege escalation vulnerability that could compromise entire virtualized environments.