CVE-2016-7154 in Xen
Summary
by MITRE
Use-after-free vulnerability in the FIFO event channel code in Xen 4.4.x allows local guest OS administrators to cause a denial of service (host crash) and possibly execute arbitrary code or obtain sensitive information via an invalid guest frame number.
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Analysis
by VulDB Data Team • 04/12/2019
The CVE-2016-7154 vulnerability represents a critical use-after-free flaw within Xen hypervisor's FIFO event channel implementation affecting versions 4.4.x. This vulnerability resides in the core virtualization infrastructure that manages communication between guest operating systems and the host hypervisor. The issue stems from improper memory management practices where freed memory blocks are still referenced or accessed by subsequent operations, creating potential exploitation vectors for malicious actors within the guest environment.
The technical exploitation of this vulnerability occurs through manipulation of guest frame numbers within the FIFO event channel code path. When a guest OS administrator submits invalid guest frame numbers, the hypervisor's event handling mechanism fails to properly validate these inputs before attempting to access previously freed memory structures. This use-after-free condition creates a scenario where attackers can potentially control the execution flow of the hypervisor, leading to either system crashes or more severe consequences including privilege escalation and information disclosure.
From an operational perspective, this vulnerability presents a significant risk to virtualized environments as it allows local guest administrators to compromise the host system's stability and security. The impact extends beyond simple denial of service since the flaw could enable arbitrary code execution within the host context, potentially allowing attackers to escape the guest environment and gain elevated privileges. The vulnerability affects the fundamental communication mechanisms between guest and host, undermining the isolation properties that virtualization platforms rely upon for security.
The attack surface for this vulnerability is particularly concerning as it requires only local access within a guest OS, making it accessible to any user with administrative privileges inside that virtual machine. This characteristic aligns with attack patterns documented in the MITRE ATT&CK framework under privilege escalation and defense evasion techniques, where attackers leverage hypervisor flaws to gain deeper system access. The vulnerability also relates to CWE-416, which specifically addresses use-after-free conditions in software development practices.
Organizations should implement immediate mitigations including patching affected Xen installations to versions 4.5.0 and later, which contain the necessary fixes for the memory management issues in the FIFO event channel implementation. Additionally, virtualization administrators should consider implementing strict guest access controls and monitoring for anomalous frame number usage patterns. The vulnerability demonstrates the critical importance of proper memory management in hypervisor code and highlights the need for comprehensive security testing of core virtualization components. Regular security assessments and vulnerability scanning should include verification of hypervisor versions and patch status to prevent exploitation of similar memory corruption vulnerabilities in the virtualization stack.