CVE-2017-15592 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x allowing x86 HVM guest OS users to cause a denial of service (hypervisor crash) or possibly gain privileges because self-linear shadow mappings are mishandled for translated guests.
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Analysis
by VulDB Data Team • 01/17/2021
The vulnerability identified as CVE-2017-15592 represents a critical flaw in the Xen hypervisor affecting versions 4.9.x and earlier, specifically impacting x86 Hardware Virtual Machine (HVM) guest operating systems. This issue stems from improper handling of self-linear shadow mappings within the hypervisor's memory management subsystem, creating a pathway for malicious guest users to exploit the system. The vulnerability operates at the intersection of virtualization security and memory management, where guest operating systems can manipulate memory mappings in ways that directly affect the hypervisor's stability and security boundaries.
The technical root cause of this vulnerability lies in the hypervisor's shadow page table management mechanism, which maintains multiple copies of page tables to facilitate memory access control between guest and host systems. When dealing with self-linear mappings, where guest virtual addresses map to the same physical addresses, the hypervisor fails to properly validate and handle these mappings during translation processes. This mismanagement occurs during the process of translating guest virtual addresses to host physical addresses, particularly when the hypervisor attempts to maintain shadow page tables that mirror the guest's memory layout. The flaw manifests when guest operating systems exploit the lack of proper validation checks in the shadow mapping code, allowing them to manipulate page table entries in ways that cause the hypervisor to crash or potentially execute arbitrary code with elevated privileges.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, encompassing potential privilege escalation and system compromise. An attacker with access to a guest operating system can trigger hypervisor crashes through carefully crafted memory access patterns, leading to service disruption across all virtual machines hosted on the same hypervisor. More critically, the vulnerability may allow privilege escalation from guest user level to hypervisor level, enabling attackers to gain control over the entire virtualization environment and potentially compromise all hosted virtual machines. This represents a fundamental breach in the isolation guarantees that virtualization platforms are designed to provide, as it allows malicious guests to escape their containment boundaries and directly affect the host system's integrity.
The exploitation of this vulnerability aligns with several ATT&CK techniques including privilege escalation and defense evasion, where attackers leverage hypervisor weaknesses to maintain persistent access and avoid detection. From a CWE perspective, this vulnerability maps to CWE-121, which deals with stack-based buffer overflows, and CWE-122, concerning heap-based buffer overflows, as the improper memory handling creates conditions where memory corruption can occur. The vulnerability also relates to CWE-248, which addresses exposed exceptions, as the hypervisor's failure to properly handle edge cases in memory mapping creates opportunities for unhandled exceptions that can lead to system crashes or privilege escalation. Organizations running Xen hypervisors must consider this vulnerability as part of their broader security posture, particularly in environments where multiple tenants share the same physical infrastructure.
Mitigation strategies for CVE-2017-15592 primarily involve immediate patching of the Xen hypervisor to versions 4.10.0 and later, which contain the necessary fixes for proper shadow mapping handling. System administrators should implement comprehensive monitoring to detect anomalous memory access patterns that might indicate exploitation attempts, particularly focusing on memory management operations within virtualized environments. Additionally, organizations should consider implementing hypervisor-level security controls such as memory access controls and privilege separation mechanisms to limit the potential impact of successful exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify other potential hypervisor weaknesses that could be exploited in combination with this vulnerability, ensuring a layered defense approach that protects against both known and emerging threats in virtualized environments.