CVE-2017-15595 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x allowing x86 PV guest OS users to cause a denial of service (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking.
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Analysis
by VulDB Data Team • 12/24/2024
The vulnerability identified as CVE-2017-15595 represents a critical flaw in the Xen hypervisor affecting versions through 4.9.x that specifically impacts x86 paravirtualized guest operating systems. This security issue stems from improper handling of page-table structures within the hypervisor's memory management subsystem, creating a pathway for malicious guest users to exploit the system through crafted page-table stacking operations. The vulnerability exists in the hypervisor's implementation of nested page table handling, where insufficient validation allows for recursive page table structures that can lead to unbounded recursion during processing.
The technical exploitation of this vulnerability occurs when a malicious x86 paravirtualized guest operating system user crafts specific page table entries that create recursive structures within the hypervisor's memory management code. This crafted page-table stacking causes the hypervisor to enter infinite recursion during page table traversal operations, consuming excessive stack space and ultimately leading to hypervisor crashes. The flaw is particularly dangerous because it can be exploited by unprivileged guest users who do not require elevated privileges to trigger the malicious behavior, making it a significant concern for multi-tenant cloud environments where guest isolation is paramount.
The operational impact of CVE-2017-15595 extends beyond simple denial of service scenarios to potentially enabling privilege escalation attacks. While the primary effect manifests as unbounded recursion and stack consumption leading to hypervisor crashes, the vulnerability's potential for privilege escalation arises from the ability to manipulate the hypervisor's memory management structures. This creates opportunities for attackers to gain elevated privileges within the virtualized environment, potentially compromising the entire host system and all virtual machines running on it. The vulnerability affects systems where Xen hypervisors are deployed in cloud computing environments, virtualization platforms, and any infrastructure relying on Xen's paravirtualized guest support.
Mitigation strategies for this vulnerability require immediate patching of affected Xen hypervisor versions to 4.10 or later, where the issue has been resolved through proper validation of page table structures and implementation of recursion depth limits. System administrators should also implement monitoring for unusual stack consumption patterns and hypervisor crash events that may indicate exploitation attempts. The vulnerability aligns with CWE-674, which addresses uncontrolled recursion in software systems, and represents a significant concern under ATT&CK technique T1059.001 for executing malicious code through hypervisor manipulation. Organizations should conduct comprehensive vulnerability assessments of their Xen deployments and ensure that all virtual machines are running patched hypervisor versions to prevent exploitation of this critical flaw.