CVE-2012-5515 in XEN
Summary
by MITRE
The (1) XENMEM_decrease_reservation, (2) XENMEM_populate_physmap, and (3) XENMEM_exchange hypercalls in Xen 4.2 and earlier allow local guest administrators to cause a denial of service (long loop and hang) via a crafted extent_order value.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2012-5515 affects the Xen hypervisor version 4.2 and earlier, specifically targeting three critical hypercalls: XENMEM_decrease_reservation, XENMEM_populate_physmap, and XENMEM_exchange. These hypercalls serve as essential interfaces between guest operating systems and the underlying hypervisor for memory management operations. The flaw stems from insufficient input validation within these hypercalls, allowing malicious guest administrators to manipulate memory allocation parameters through crafted extent_order values that can trigger unintended system behavior.
The technical implementation of this vulnerability exploits a lack of proper bounds checking and parameter validation in the memory management subsystem of Xen. When a guest administrator submits a malicious extent_order value to any of these three hypercalls, the hypervisor enters into an extended processing loop that consumes excessive CPU resources and ultimately leads to system hang conditions. This occurs because the hypervisor's memory management code fails to properly validate the extent_order parameter, which determines the size and scope of memory allocation operations. The flaw manifests as a denial of service condition where legitimate system operations become blocked while the hypervisor remains trapped in an infinite loop processing the malformed input.
From an operational impact perspective, this vulnerability represents a significant security concern for virtualized environments as it allows local guest administrators to disrupt system availability without requiring elevated privileges. The attack vector is particularly dangerous because it can be executed from within a guest operating system, making it difficult to detect and prevent through traditional network-based security measures. The resulting denial of service affects not only the compromised guest but potentially impacts the entire virtualization platform, as the hypervisor's resources become unavailable for other virtual machines running on the same physical host. This vulnerability can be exploited to create persistent availability issues that may go unnoticed for extended periods, especially in environments where guest administrators have legitimate access rights.
The vulnerability aligns with CWE-129, which addresses improper validation of array index values, and falls under the ATT&CK technique T1499.004 for Network Denial of Service. Organizations should implement immediate mitigation strategies including upgrading to Xen versions 4.3 or later where these vulnerabilities have been addressed through proper input validation and bounds checking mechanisms. System administrators should also consider implementing monitoring solutions that can detect anomalous memory management operations and establish guest access controls that limit administrative privileges to only trusted users. Additionally, regular security assessments of virtualization environments should include verification of hypervisor versions and patch status to prevent exploitation of known vulnerabilities that could lead to system-wide availability disruption.