CVE-2017-17565 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x allowing PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17565 represents a critical flaw in the Xen hypervisor affecting versions through 4.9.x that enables malicious guest operating system users to execute a denial of service attack against the host system. This vulnerability specifically targets systems utilizing paravirtualized (PV) guest operating systems where both shadow mode and log-dirty mode are active, creating a dangerous condition that can result in complete host OS crashes. The flaw stems from an incorrect assertion within the memory management subsystem of Xen, particularly concerning the Machine to Physical (M2P) mapping functionality that is fundamental to hypervisor memory management operations.
The technical root cause of this vulnerability lies in the improper handling of memory mapping assertions within Xen's shadow page table implementation. When shadow mode and log-dirty mode are simultaneously enabled, the hypervisor's assertion mechanism fails to properly validate the consistency of Machine to Physical mapping entries. This assertion failure occurs during memory management operations where guest OS users can manipulate memory mappings in ways that trigger the faulty assertion, leading to a kernel panic and subsequent host system crash. The vulnerability is particularly dangerous because it allows unprivileged guest users to exploit a condition that should be protected against by the hypervisor's memory management controls, effectively bypassing security boundaries between guest and host environments.
From an operational impact perspective, this vulnerability presents a severe risk to cloud infrastructure and virtualized environments that rely on Xen hypervisors. Organizations running multiple virtual machines on a single host system face significant operational disruption when this vulnerability is exploited, as a single compromised guest can potentially crash the entire host system and affect all other virtual machines running on that physical hardware. The attack vector requires minimal privileges from the guest side, making it particularly concerning for multi-tenant cloud environments where different users may have access to shared infrastructure. The vulnerability essentially undermines the fundamental security principle of hypervisor isolation, allowing guest users to directly impact host system stability and availability.
The mitigation strategies for this vulnerability involve immediate patching of Xen hypervisor installations to versions that address the incorrect assertion handling in M2P mapping operations. System administrators should also consider disabling shadow mode and log-dirty mode combinations when these features are not strictly required for performance optimization. Additionally, implementing monitoring solutions that can detect unusual memory management patterns and potential exploitation attempts can provide early warning capabilities. From a security framework perspective, this vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and relates to ATT&CK technique T1068 (Exploitation for Privilege Escalation) when considering the broader attack surface. Organizations should also conduct comprehensive security assessments of their virtualization environments to identify other potential vulnerabilities in hypervisor configurations that could be exploited in similar manners, particularly focusing on memory management and assertion handling mechanisms that are critical to hypervisor stability and security boundaries.
This vulnerability demonstrates the critical importance of proper memory management validation in hypervisor implementations and highlights the potential for guest users to exploit seemingly benign memory management features to achieve host-level compromise. The flaw serves as a reminder of the complex security considerations inherent in virtualization environments where the hypervisor must maintain strict isolation between multiple operating systems while providing necessary performance optimizations that can introduce new attack vectors when not properly validated.