CVE-2017-15594 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x allowing x86 SVM PV guest OS users to cause a denial of service (hypervisor crash) or gain privileges because IDT settings are mishandled during CPU hotplugging.
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Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2017-15594 represents a critical flaw in the Xen hypervisor affecting versions through 4.9.x that specifically impacts x86 System Virtual Machine (SVM) ParaVirtualized (PV) guest operating systems. This issue stems from improper handling of Interrupt Descriptor Table (IDT) settings during CPU hotplugging operations, creating a pathway for malicious guest users to either crash the hypervisor or escalate their privileges. The flaw exists within the hypervisor's management of interrupt handling mechanisms when virtual CPUs are dynamically added or removed from the system, fundamentally compromising the isolation guarantees that hypervisors must maintain between guest environments and the host system.
The technical root cause of this vulnerability lies in the improper synchronization and management of IDT entries when CPU hotplugging occurs in SVM PV guests. During normal operation, the hypervisor maintains precise control over interrupt handling mechanisms to ensure that guest operating systems cannot directly access or manipulate critical system resources. However, when CPU hotplugging is initiated, the hypervisor fails to properly update or validate IDT configurations for newly added virtual processors, creating a window where malicious code within the guest can exploit this inconsistency. This mismanagement allows the guest to manipulate interrupt vectors in ways that can either trigger hypervisor crashes through invalid interrupt handling or potentially execute code with elevated privileges by bypassing normal access controls.
The operational impact of CVE-2017-15594 extends beyond simple denial of service scenarios, as it presents a privilege escalation vector that could enable attackers to gain unauthorized access to hypervisor-level functionality. When exploited, this vulnerability can cause complete hypervisor crashes that result in service disruption across all virtual machines hosted on the affected system, while the privilege escalation component could allow malicious users to execute arbitrary code with the highest system privileges. This represents a fundamental breakdown in hypervisor security isolation, as the vulnerability enables guest users to affect the integrity and availability of the host system itself. The impact is particularly severe in cloud computing environments where multiple tenants share the same hypervisor infrastructure, as a single compromised guest could potentially affect all other virtual machines running on the same host.
Mitigation strategies for CVE-2017-15594 require immediate patching of affected Xen hypervisor versions to the patched releases that properly handle IDT settings during CPU hotplugging operations. Organizations should also implement monitoring solutions to detect unusual CPU hotplugging activities that might indicate exploitation attempts. Security teams should consider disabling CPU hotplugging functionality in environments where this vulnerability cannot be immediately patched, though this approach may impact system flexibility and performance. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception," and maps to ATT&CK technique T1059 for privilege escalation through hypervisor manipulation. Organizations should also review their virtualization security configurations and implement proper isolation measures between guest environments to limit the potential impact of such vulnerabilities. Regular security assessments of virtualization environments are essential to identify and remediate similar issues before they can be exploited by adversaries.