CVE-2016-10013 in Xen
Summary
by MITRE
Xen through 4.8.x allows local 64-bit x86 HVM guest OS users to gain privileges by leveraging mishandling of SYSCALL singlestep during emulation.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-10013 affects the Xen hypervisor version 4.8.x and earlier, presenting a significant privilege escalation risk for local users within 64-bit x86 HVM guest operating systems. This flaw resides in the hypervisor's emulation handling of SYSCALL instructions during singlestep execution, creating a critical security gap that adversaries can exploit to elevate their privileges from guest user level to host system privileges. The vulnerability specifically targets the interaction between the hypervisor's emulation layer and the guest operating system's execution environment, where proper handling of system call instructions fails during debugging or single stepping operations.
The technical root cause of this vulnerability stems from improper state management within the Xen hypervisor's emulation subsystem when processing SYSCALL instructions in singlestep mode. During singlestep execution, the hypervisor must carefully manage the transition between guest and host execution contexts while maintaining proper privilege levels and instruction flow. When a 64-bit x86 HVM guest executes a SYSCALL instruction and the hypervisor attempts to singlestep through this instruction, the emulation logic fails to properly account for the privilege level transitions and register state modifications that should occur during system call processing. This mismanagement creates an opportunity for malicious code within the guest environment to manipulate the hypervisor's internal state, ultimately allowing privilege escalation.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the security isolation that hypervisors are designed to maintain between guest operating systems and the host system. Local users within a 64-bit x86 HVM guest can leverage this flaw to execute arbitrary code with host-level privileges, potentially leading to complete system compromise and unauthorized access to all resources managed by the hypervisor. This vulnerability is particularly concerning in multi-tenant cloud environments where multiple guests share the same physical hardware, as it could enable one guest to access or manipulate resources belonging to other guests or the host system itself. The privilege escalation occurs without requiring any special permissions or external attack vectors, making it a particularly dangerous flaw in virtualized environments.
Security professionals should implement immediate mitigations including upgrading to Xen hypervisor versions 4.8.1 or later, which contain the necessary patches to address the SYSCALL singlestep emulation handling issue. Organizations should also consider implementing additional monitoring and logging of hypervisor activities to detect potential exploitation attempts. The vulnerability aligns with CWE-119 Improper Access Control and CWE-284 Improper Access Control, as it represents a failure in privilege management and access control mechanisms within the virtualization layer. From an ATT&CK framework perspective, this vulnerability maps to T1055 Process Injection and T1068 Local Privilege Escalation, as it enables local users to escalate their privileges through manipulation of hypervisor emulation behavior. The mitigation strategy should include comprehensive testing of patched hypervisor versions in staging environments before production deployment to ensure compatibility and stability of virtualized workloads.