CVE-2007-6416 in Xen
Summary
by MITRE
The copy_to_user function in the PAL emulation functionality for Xen 3.1.2 and earlier, when running on ia64 systems, allows HVM guest users to access arbitrary physical memory by triggering certain mapping operations.
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Analysis
by VulDB Data Team • 08/04/2019
The vulnerability described in CVE-2007-6416 represents a critical security flaw within the Xen hypervisor's PAL (Processor Abstraction Layer) emulation subsystem. This issue specifically affects Xen versions 3.1.2 and earlier when operating on ia64 (Itanium) architecture systems. The vulnerability stems from improper memory management within the copy_to_user function, which is responsible for transferring data between the hypervisor and guest operating systems. The flaw enables malicious HVM (Hardware Virtual Machine) guest users to bypass normal memory access restrictions and directly access physical memory addresses that should otherwise be protected from guest-level access.
The technical implementation of this vulnerability exploits the PAL emulation functionality that serves as a bridge between the virtualized hardware environment and the underlying physical processor capabilities. When HVM guests execute certain mapping operations, the copy_to_user function fails to properly validate memory access permissions, allowing guest users to craft specific memory access patterns that can traverse the hypervisor's memory protection boundaries. This creates a direct pathway for guest users to read or write to arbitrary physical memory locations, effectively breaking the isolation that virtualization is designed to maintain between different guest environments and the host system.
The operational impact of this vulnerability is severe and far-reaching within virtualized environments. An attacker with access to an HVM guest could potentially extract sensitive information from other virtual machines running on the same host, access host system memory to retrieve credentials or encryption keys, or even modify critical system components. This represents a complete breakdown of the hypervisor's security model and could lead to full system compromise. The vulnerability affects not only the integrity and confidentiality of virtualized environments but also undermines the fundamental security assumptions that organizations rely upon when implementing virtualization technologies.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-125: "Out-of-bounds Read" and CWE-264: "Permissions, Privileges, and Access Controls" categories, demonstrating how improper memory access controls can lead to privilege escalation and information disclosure. The attack vector maps to ATT&CK technique T1055: "Process Injection" and T1082: "System Information Discovery" as attackers could leverage this flaw to gain unauthorized access to system memory and extract sensitive data. The vulnerability also relates to T1496: "Resource Hijacking" since it could enable attackers to consume host resources or manipulate system behavior through direct physical memory access.
Mitigation strategies for this vulnerability require immediate patching of affected Xen hypervisor versions to 3.1.3 or later, where the PAL emulation functionality has been corrected to properly validate memory access permissions. Organizations should implement additional monitoring to detect unusual memory access patterns from HVM guests and consider isolating critical systems on separate hypervisor instances. Network segmentation and access controls should be strengthened to limit potential lateral movement if exploitation occurs. System administrators should also conduct thorough security assessments of their virtualization environments to identify other potential vulnerabilities that might exist in similar components or subsystems. Regular updates and patch management processes must be prioritized to ensure that hypervisor installations remain protected against known vulnerabilities.