CVE-2012-4537 in Xen
Summary
by MITRE
Xen 3.4 through 4.2, and possibly earlier versions, does not properly synchronize the p2m and m2p tables when the set_p2m_entry function fails, which allows local HVM guest OS administrators to cause a denial of service (memory consumption and assertion failure), aka "Memory mapping failure DoS vulnerability."
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Analysis
by VulDB Data Team • 04/19/2021
The vulnerability identified as CVE-2012-4537 represents a critical synchronization flaw within the Xen hypervisor's memory management subsystem that affects versions 3.4 through 4.2 and potentially earlier releases. This issue manifests in the hypervisor's handling of page-to-machine (p2m) and machine-to-page (m2p) table operations, which are fundamental components of virtual memory management in virtualized environments. The core problem arises from inadequate synchronization mechanisms when the set_p2m_entry function encounters failure conditions, creating a scenario where malicious or compromised guest operating systems can exploit this weakness to disrupt normal system operations.
The technical flaw stems from the hypervisor's failure to properly maintain consistency between p2m and m2p tables during error conditions within the set_p2m_entry function. When this function fails to complete its operation successfully, the synchronization between these critical memory mapping tables becomes corrupted. This inconsistency creates opportunities for local administrators within HVM (Hardware Virtual Machine) guest operating systems to manipulate memory mappings in ways that can trigger assertion failures and consume excessive system resources. The vulnerability specifically targets the memory management layer where the hypervisor translates virtual addresses between guest and host memory spaces, making it particularly dangerous as it operates at the core of virtualization security boundaries.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise the stability and availability of entire virtualized environments. Local HVM guest administrators can leverage this weakness to cause memory consumption anomalies that may lead to system crashes or complete system unresponsiveness. The assertion failures that occur as a result of this synchronization failure can cause the hypervisor to terminate unexpectedly, leading to service disruption for all virtual machines hosted on the affected system. This vulnerability is particularly concerning in multi-tenant cloud environments where guest administrators might exploit it to affect other users' virtual machines or to cause broader system instability that impacts the entire infrastructure.
Mitigation strategies for CVE-2012-4537 require immediate patching of affected Xen hypervisor versions to address the synchronization issues within the p2m and m2p table management functions. Organizations should prioritize updating to versions that contain fixes for this specific synchronization flaw, typically found in Xen 4.3 and later releases. Additionally, implementing monitoring solutions that can detect unusual memory consumption patterns or assertion failures in hypervisor processes provides early warning capabilities. Network segmentation and access controls should be reinforced to limit the potential impact of compromised guest administrators, while regular security audits of virtualization environments help identify and remediate similar synchronization issues. This vulnerability aligns with CWE-362, which addresses race conditions in concurrent systems, and maps to ATT&CK technique T1499.004 for denial of service attacks targeting system resources. The remediation process should include thorough testing of updated hypervisor versions in staging environments to ensure compatibility with existing virtual machine configurations before deployment to production systems.