CVE-2015-8340 in Xen
Summary
by MITRE
The memory_exchange function in common/memory.c in Xen 3.2.x through 4.6.x does not properly release locks, which might allow guest OS administrators to cause a denial of service (deadlock or host crash) via unspecified vectors, related to XENMEM_exchange error handling.
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Analysis
by VulDB Data Team • 06/30/2022
The vulnerability identified as CVE-2015-8340 resides within the memory_exchange function located in common/memory.c of the Xen hypervisor across versions 3.2.x through 4.6.x. This flaw represents a critical security issue that affects the fundamental memory management operations within the virtualization environment. The vulnerability specifically targets the improper release of locks during error handling scenarios, creating a condition where guest operating system administrators can manipulate the hypervisor's memory management subsystem to induce system instability. The issue stems from inadequate lock management within the XENMEM_exchange error handling mechanism, which is a core component responsible for memory exchange operations between guest and host systems.
The technical flaw manifests when the memory_exchange function fails to properly release locks after encountering errors during memory exchange operations. This lock release failure creates a potential deadlock condition where the hypervisor's memory management subsystem becomes permanently blocked, unable to process additional memory requests. The vulnerability is particularly dangerous because it can be exploited by guest OS administrators who have access to the virtualized environment, allowing them to leverage their privileges to cause a denial of service condition. The unspecified vectors mentioned in the description suggest that multiple attack paths exist through which an attacker can trigger the flawed error handling code path, making the vulnerability particularly insidious as it may be difficult to predict or prevent completely.
From an operational impact perspective, this vulnerability poses significant risks to virtualized environments that rely on Xen hypervisors for their infrastructure. The potential for either deadlock conditions or complete host crashes means that systems running affected Xen versions could experience unplanned outages, service disruptions, and loss of availability for all virtual machines hosted on the compromised system. The vulnerability essentially allows a malicious guest administrator to escalate their privileges and cause system-wide instability, potentially affecting multiple virtual machines simultaneously. This type of vulnerability is particularly concerning in cloud computing environments where multiple tenants share the same physical infrastructure, as it could enable one tenant to disrupt services for other tenants on the same host system.
The exploitation of this vulnerability aligns with several ATT&CK framework techniques, particularly those related to privilege escalation and denial of service. The ability for guest administrators to cause host-level crashes or deadlocks represents a significant escalation of privileges from the guest to the host level. From a CWE perspective, this vulnerability maps to CWE-667, which describes inadequate lock management, and potentially CWE-121, which covers stack-based buffer overflow conditions. The improper lock release creates a condition where the system's resource management becomes compromised, leading to the described denial of service outcomes. Organizations using Xen hypervisors in production environments must understand that this vulnerability represents a serious threat to system availability and stability, as it can be triggered through legitimate memory management operations that occur during normal system operation.
Mitigation strategies for this vulnerability primarily involve applying the official security patches released by the Xen Project, which address the improper lock release in the memory_exchange function. System administrators should immediately upgrade to Xen versions 4.7.0 or later where this vulnerability has been resolved through proper lock management implementation. Additionally, organizations should implement monitoring systems to detect unusual memory management patterns that might indicate exploitation attempts. Network segmentation and access control measures can help limit the potential impact by restricting guest administrator privileges where possible. The vulnerability also highlights the importance of thorough testing of hypervisor components, particularly around error handling paths, as the issue occurred within a function that handles critical memory operations. Organizations should conduct regular security assessments of their virtualization infrastructure to identify similar lock management issues that might exist in other components of their hypervisor environment.