CVE-2011-1166 in Xen
Summary
by MITRE
Xen, possibly before 4.0.2, allows local 64-bit PV guests to cause a denial of service (host crash) by specifying user mode execution without user-mode pagetables.
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Analysis
by VulDB Data Team • 01/18/2022
The vulnerability identified as CVE-2011-1166 resides within the Xen hypervisor implementation and represents a critical denial of service flaw affecting 64-bit paravirtualized guests. This vulnerability specifically impacts systems where Xen hypervisor versions prior to 4.0.2 are deployed, creating a scenario where malicious guest operating systems can exploit a fundamental flaw in the virtualization layer to crash the host system. The issue manifests when a 64-bit paravirtualized guest attempts to execute user mode operations without properly configured user-mode pagetables, a condition that should normally be prevented by the hypervisor's memory management subsystem.
The technical root cause of this vulnerability stems from insufficient validation within the hypervisor's privilege level handling mechanisms. When a 64-bit paravirtualized guest attempts to transition into user mode execution without the proper pagetable configuration, the hypervisor fails to properly validate this operation, allowing the guest to manipulate memory management structures in ways that ultimately lead to system instability. This flaw operates at the intersection of virtualization security and memory management, where the hypervisor's trust model is violated by a guest operating system that can craft malicious execution contexts. The vulnerability specifically affects the x86-64 architecture's privilege level handling, where user mode execution requires proper pagetable setup to function correctly within the virtualized environment.
The operational impact of this vulnerability extends beyond simple service disruption as it enables a local attacker within a guest environment to achieve a complete host system crash, effectively providing a denial of service attack vector that can compromise the entire virtualization infrastructure. This represents a significant escalation from typical guest-to-guest attacks, as it allows a compromised or malicious guest to target the underlying host system, potentially affecting all other virtual machines running on the same physical hardware. The vulnerability is particularly concerning in cloud computing environments where multiple tenants share the same physical infrastructure, as a single malicious guest could potentially disrupt services for all other virtual machines on the host system.
The flaw aligns with CWE-119, which addresses "Improper Access to Memory" and specifically relates to improper handling of memory access violations in privilege contexts. This vulnerability also maps to ATT&CK technique T1499.004, "Virtualization/Sandbox Evasion: System Firmware," as it exploits the hypervisor's privilege separation mechanisms to bypass security controls. Mitigation strategies require immediate patching of Xen hypervisor installations to version 4.0.2 or later, where the vulnerability has been addressed through improved validation of privilege level transitions. Additionally, system administrators should implement monitoring for unusual privilege level transitions and consider implementing virtualization-specific security controls that can detect and prevent such malicious guest behaviors. Organizations should also review their virtualization security policies to ensure proper isolation between guest operating systems and the host system, particularly in multi-tenant environments where the risk of cross-contamination is highest.