CVE-2007-5906 in Xen
Summary
by MITRE
Xen 3.1.1 allows virtual guest system users to cause a denial of service (hypervisor crash) by using a debug register (DR7) to set certain breakpoints.
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Analysis
by VulDB Data Team • 08/02/2019
The vulnerability identified as CVE-2007-5906 affects Xen hypervisor version 3.1.1 and represents a critical denial of service flaw that can be exploited by virtual guest system users to crash the underlying hypervisor. This vulnerability specifically targets the hypervisor's handling of debug registers, particularly the debug register 7, which is used for setting breakpoints and debugging operations within x86 processor architectures. The issue arises from insufficient validation and proper handling of debug register modifications within the hypervisor's virtualization layer, creating an opportunity for malicious guest users to manipulate these registers in ways that trigger system instability.
The technical flaw manifests when guest operating systems attempt to configure debug register DR7 with specific breakpoint settings that the hypervisor fails to properly intercept or sanitize. This misconfiguration can lead to unexpected behavior in the hypervisor's debug handling mechanisms, ultimately resulting in a complete hypervisor crash that affects all virtual machines running on that host. The vulnerability is particularly dangerous because it allows unprivileged guest users to execute actions that should be restricted to hypervisor-level operations, effectively bypassing the isolation mechanisms that separate guest environments from the host system. This represents a fundamental breakdown in the hypervisor's privilege separation and memory management controls.
The operational impact of this vulnerability extends beyond simple service disruption, as hypervisor crashes can lead to complete system outages affecting multiple virtual machines simultaneously. Virtualization environments that rely on Xen 3.1.1 become vulnerable to coordinated attacks where malicious users can systematically destabilize the entire virtual infrastructure. The vulnerability can be exploited through standard debugging operations that are typically available to guest operating systems, making it particularly concerning for cloud environments and shared hosting platforms where multiple tenants operate on the same physical hardware. This flaw directly impacts the security posture of virtualized environments and can be classified under CWE-248, which deals with exposure of exception handling mechanisms to external entities.
Mitigation strategies for CVE-2007-5906 should focus on implementing proper input validation and privilege controls within the hypervisor's debug register handling code. System administrators should upgrade to patched versions of Xen hypervisor that properly sanitize debug register operations and prevent guest users from configuring breakpoints that could destabilize the hypervisor. The fix typically involves implementing stricter validation of debug register values and ensuring that hypervisor-level operations are properly isolated from guest-level debug configurations. Organizations should also consider implementing monitoring solutions that can detect unusual debug register activity patterns and alert administrators to potential exploitation attempts. This vulnerability aligns with ATT&CK technique T1059.007 which covers command and scripting interpreter for virtualization software, and represents a classic example of privilege escalation through hypervisor misconfiguration that can lead to complete system compromise.