CVE-2018-19964 in Xen
Summary
by MITRE
An issue was discovered in Xen 4.11.x allowing x86 guest OS users to cause a denial of service (host OS hang) because the p2m lock remains unavailable indefinitely in certain error conditions.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 04/19/2020
The vulnerability identified as CVE-2018-19964 represents a critical denial of service weakness within the Xen virtualization platform affecting versions 4.11.x. This issue specifically targets the x86 guest operating systems and exploits a flaw in the page-to-machine (p2m) lock mechanism that governs memory management within virtualized environments. The vulnerability stems from improper handling of error conditions during memory mapping operations, creating a scenario where the p2m lock becomes permanently unavailable. This condition fundamentally compromises the host operating system's ability to manage memory resources effectively, leading to complete system hang and denial of service for all virtual machines running on the affected host. The flaw exists at the core of Xen's memory management subsystem, where the lock mechanism fails to release properly under specific error states, creating a deadlock condition that cannot be resolved without manual intervention or system reboot.
The technical implementation of this vulnerability involves the improper synchronization of memory management operations within the hypervisor layer. When guest operating systems perform certain memory mapping operations, particularly those involving page table modifications or memory allocation requests, the p2m lock mechanism encounters error conditions that prevent it from being released. This lock is essential for maintaining consistency in the page-to-machine mapping tables that translate guest virtual addresses to host physical addresses. According to CWE-362, this vulnerability demonstrates a classic concurrent programming flaw where a lock is not properly released, leading to a race condition scenario that can be exploited by malicious guest users. The flaw manifests when the error handling code path fails to execute the necessary unlock operations, leaving the lock in a held state indefinitely. This behavior violates fundamental principles of resource management and synchronization protocols that are critical for maintaining system stability in virtualized environments.
The operational impact of CVE-2018-19964 extends beyond simple service disruption to potentially catastrophic system failures within virtualized infrastructures. Host operating systems experiencing this vulnerability become completely unresponsive, rendering all virtual machines hosted on that system inaccessible and effectively deadlocked. Attackers with access to guest operating systems can exploit this weakness to perform persistent denial of service attacks against virtualized environments, particularly in cloud computing scenarios where multiple tenants share the same physical infrastructure. The vulnerability is particularly dangerous in multi-tenant environments such as public cloud services, where a single malicious guest could compromise the entire host system and affect all other virtual machines running on the same physical hardware. This represents a significant security concern under the ATT&CK framework's privilege escalation and denial of service tactics, as it allows attackers to leverage guest-level access to achieve host-level disruption. The impact is amplified in enterprise virtualization environments where business-critical applications depend on stable hypervisor performance.
Mitigation strategies for CVE-2018-19964 require immediate implementation of the vendor-provided patches and updates to Xen versions that address the specific p2m lock handling issues. Organizations should prioritize updating their Xen hypervisor installations to versions that contain the corrected error handling routines for memory management operations. System administrators should implement monitoring solutions to detect unusual lock contention patterns that might indicate exploitation attempts. The recommended approach includes applying the security patches immediately while maintaining backup procedures for system recovery in case of update failures. Additionally, implementing proper isolation measures between guest operating systems can help limit the potential impact of exploitation attempts. Organizations should also consider implementing network segmentation and access controls to reduce the attack surface available to potential attackers. The vulnerability highlights the importance of thorough testing of error handling code paths in hypervisor implementations, as proper resource management is fundamental to maintaining system stability and preventing exploitation of synchronization flaws. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other hypervisor components and ensure comprehensive protection against similar attack vectors.