CVE-2017-10918 in Xen
Summary
by MITRE
Xen through 4.8.x does not validate memory allocations during certain P2M operations, which allows guest OS users to obtain privileged host OS access, aka XSA-222.
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Analysis
by VulDB Data Team • 12/30/2020
The vulnerability identified as CVE-2017-10918 represents a critical security flaw in the Xen hypervisor affecting versions 4.8.x and earlier. This issue stems from inadequate validation of memory allocations during specific P2M (Page to Machine) operations within the hypervisor's memory management subsystem. The flaw allows malicious guest operating system users to escalate privileges and gain unauthorized access to the underlying host operating system, creating a severe escalation of privileges vulnerability that undermines the fundamental security isolation provided by virtualization technologies.
The technical root cause of this vulnerability lies in the improper validation mechanisms within Xen's memory management operations. During P2M translation processes, the hypervisor fails to properly verify the legitimacy of memory allocation requests from guest VMs. This validation gap enables attackers to manipulate memory mappings in ways that should be restricted to privileged hypervisor components only. The vulnerability specifically affects the hypervisor's handling of page table operations and memory allocation routines that are critical for maintaining the isolation boundary between guest VMs and the host system. According to CWE classification, this represents a weakness in validation of memory allocation operations, specifically CWE-129, which deals with insufficient validation of length of input buffers.
The operational impact of CVE-2017-10918 is severe and far-reaching within virtualized environments. Attackers exploiting this vulnerability can achieve arbitrary code execution on the host system with the privileges of the hypervisor itself, potentially leading to complete system compromise. This allows for the theft of sensitive data, persistent backdoor installation, and the ability to manipulate other VMs running on the same host. The vulnerability is particularly dangerous in cloud computing environments where multiple tenants share the same physical infrastructure, as a single compromised guest VM could potentially compromise the entire host and all other VMs hosted on it. The attack vector requires only guest-level access, making it easily exploitable in environments where guest VMs are not properly isolated or where users have legitimate access to virtual machines.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected Xen hypervisor versions to 4.8.1 or later, which contains the necessary fixes for the memory allocation validation issues. Organizations should also implement additional monitoring and detection measures to identify potential exploitation attempts, including anomaly detection for unusual memory allocation patterns and unauthorized access attempts. Network segmentation and access controls should be strengthened to limit guest VM access to potentially vulnerable hypervisor interfaces. The mitigation approach aligns with ATT&CK framework techniques related to privilege escalation and defense evasion, emphasizing the importance of maintaining hypervisor integrity and implementing proper access controls. System administrators should also conduct thorough security assessments of their virtualization environments to identify any other potential vulnerabilities that could be exploited in conjunction with this flaw.