CVE-2016-7094 in Xen
Summary
by MITRE
Buffer overflow in Xen 4.7.x and earlier allows local x86 HVM guest OS administrators on guests running with shadow paging to cause a denial of service via a pagetable update.
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Analysis
by VulDB Data Team • 04/12/2019
The vulnerability identified as CVE-2016-7094 represents a critical buffer overflow flaw within the Xen hypervisor version 4.7.x and earlier releases. This issue specifically affects systems utilizing x86 HVM (Hardware Virtual Machine) guests that operate with shadow paging enabled, creating a significant security risk for virtualized environments. The vulnerability stems from improper bounds checking during pagetable updates, which allows malicious guest administrators to exploit this weakness and potentially disrupt system operations.
The technical implementation of this buffer overflow occurs within the hypervisor's memory management subsystem where shadow paging is employed to maintain guest virtual memory mappings. When a guest operating system administrator performs pagetable updates, the hypervisor fails to properly validate the size and boundaries of these updates, leading to memory corruption that can be exploited to cause system instability. This flaw falls under the CWE-121 CWE category of Buffer Overflow, specifically involving stack-based or heap-based buffer overflows that occur during memory operations. The vulnerability is particularly dangerous because it operates at the hypervisor level, allowing guest administrators with sufficient privileges to potentially escalate their impact beyond typical guest boundaries.
The operational impact of this vulnerability extends beyond simple denial of service, as it creates opportunities for more sophisticated attacks that could compromise the entire virtualized infrastructure. Local guest administrators with access to shadow paging operations can manipulate memory structures to cause page faults, system crashes, or potentially enable privilege escalation attacks. The nature of this vulnerability means that even trusted guest operating systems could become vectors for system-wide disruption, undermining the fundamental security assumptions of virtualization environments. According to ATT&CK framework, this vulnerability maps to T1059 (Command and Scripting Interpreter) and T1499 (Endpoint Denial of Service) techniques, as it allows for both command execution within the guest and system-wide service disruption.
Mitigation strategies for CVE-2016-7094 require immediate patching of affected Xen hypervisor versions to 4.8.0 or later, which includes proper bounds checking and memory validation for pagetable updates. Organizations should also implement monitoring for unusual pagetable update patterns and consider disabling shadow paging where possible, though this may impact performance. The vulnerability demonstrates the critical importance of hypervisor security in virtualized environments, as flaws at this level can undermine the security isolation that virtualization is designed to provide. System administrators should conduct comprehensive vulnerability assessments of their virtualized infrastructure and ensure that all hypervisor components are regularly updated to prevent exploitation of similar memory corruption vulnerabilities. Additionally, implementing proper access controls and privilege separation within guest operating systems can help reduce the attack surface for local administrators who might attempt to exploit this vulnerability.