CVE-2019-17342 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges by leveraging a race condition that arose when XENMEM_exchange was introduced.
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Analysis
by VulDB Data Team • 09/27/2020
The vulnerability identified as CVE-2019-17342 represents a critical race condition flaw within the Xen hypervisor version 4.11.x and earlier, specifically affecting x86 paravirtualized guest operating systems. This issue stems from improper handling of memory management operations during the XENMEM_exchange hypercall implementation, creating a window where malicious guest users can exploit temporal inconsistencies in the hypervisor's memory management subsystem. The race condition manifests when multiple threads or processes attempt to access shared memory resources simultaneously, leading to unpredictable behavior that can be weaponized for system compromise.
The technical exploitation of this vulnerability occurs through the manipulation of the XENMEM_exchange hypercall, which is designed to exchange memory pages between guest and hypervisor contexts. When concurrent access patterns are introduced during this exchange operation, the hypervisor fails to properly synchronize memory state transitions, allowing a malicious paravirtualized guest user to manipulate memory mappings in ways that could lead to privilege escalation or system instability. This flaw operates at the intersection of hypervisor memory management and concurrency control mechanisms, making it particularly dangerous as it can be triggered from within guest operating systems without requiring elevated privileges.
The operational impact of CVE-2019-17342 extends beyond simple denial of service scenarios, as it provides potential pathways for privilege escalation attacks that could allow guest users to break out of their isolated virtual environments and gain unauthorized access to the underlying host system or other virtual machines. This vulnerability directly relates to CWE-362, which describes race conditions in software implementations, and aligns with ATT&CK technique T1055.011 for privilege escalation through hypervisor manipulation. The vulnerability affects systems running Xen hypervisors in production environments where multiple virtual machines share the same physical host, creating potential for widespread compromise across virtualized infrastructures.
Mitigation strategies for CVE-2019-17342 require immediate patching of affected Xen hypervisor versions to 4.12.0 and later, which includes proper synchronization mechanisms for memory exchange operations. System administrators should implement strict monitoring of hypervisor memory operations and consider isolating critical workloads on patched systems. The vulnerability demonstrates the importance of proper concurrency control in hypervisor implementations and highlights the need for comprehensive testing of memory management operations under stress conditions. Organizations should also review their virtualization security policies and consider implementing additional isolation measures beyond standard virtual machine boundaries to prevent potential exploitation of similar race condition vulnerabilities in other hypervisor components.