CVE-2014-9066 in Xen
Summary
by MITRE
Xen 4.4.x and earlier, when using a large number of VCPUs, does not properly handle read and write locks, which allows local x86 guest users to cause a denial of service (write denial or NMI watchdog timeout and host crash) via a large number of read requests, a different vulnerability than CVE-2014-9065.
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Analysis
by VulDB Data Team • 03/01/2022
The vulnerability identified as CVE-2014-9066 affects Xen hypervisor versions 4.4.x and earlier, specifically when systems utilize a large number of virtual CPUs. This issue represents a significant concurrency problem within the hypervisor's locking mechanisms that can be exploited by local users within x86 guest operating systems to cause system instability. The flaw manifests when the hypervisor fails to properly manage read and write locks during high-concurrency scenarios involving numerous virtual CPUs, creating a condition where legitimate system operations can be disrupted through carefully crafted workloads.
The technical implementation of this vulnerability stems from improper handling of concurrent access patterns within the hypervisor's memory management subsystem. When multiple virtual CPUs attempt to perform read operations simultaneously, the locking mechanism becomes overwhelmed, leading to potential deadlock conditions or excessive lock contention. This improper lock management creates a scenario where the system becomes unresponsive to legitimate write operations, effectively causing a denial of service condition. The vulnerability is particularly dangerous because it can trigger NMI (Non-Maskable Interrupt) watchdog timeouts, which are designed to detect system hangs and can ultimately result in complete host system crashes. The flaw operates through a different attack vector than CVE-2014-9065, indicating separate but related concurrency issues within the hypervisor's resource management.
From an operational perspective, this vulnerability presents a serious risk to virtualized environments where multiple guest operating systems share a single physical host. Local users within any x86 guest can exploit this condition to disrupt services on the host system, potentially affecting all virtual machines running on that hardware. The impact extends beyond simple service disruption to include potential complete system crashes that could compromise the availability of critical infrastructure. The vulnerability is particularly concerning in cloud computing environments and server consolidation scenarios where high CPU utilization and multiple virtual CPUs are common. The attack requires only local access within a guest environment, making it accessible to any user with basic privileges within that virtual machine, which significantly increases the attack surface and potential for exploitation.
Organizations should prioritize patching affected Xen hypervisor versions to address this vulnerability, as the remediation involves updating to versions that properly handle concurrent read and write lock operations. System administrators should also implement monitoring for unusual lock contention patterns and NMI watchdog timeouts that could indicate exploitation attempts. The vulnerability aligns with CWE-362, which describes concurrency issues related to improper locking mechanisms, and can be categorized under ATT&CK technique T1499.001 for network denial of service attacks. Additional mitigations include limiting the number of VCPUs assigned to individual virtual machines when possible, implementing proper resource isolation between guests, and maintaining robust intrusion detection systems that can identify unusual patterns of lock contention or system timeouts that may indicate exploitation attempts.