CVE-2015-8338 in Xen
Summary
by MITRE
Xen 4.6.x and earlier does not properly enforce limits on page order inputs for the (1) XENMEM_increase_reservation, (2) XENMEM_populate_physmap, (3) XENMEM_exchange, and possibly other HYPERVISOR_memory_op suboperations, which allows ARM guest OS administrators to cause a denial of service (CPU consumption, guest reboot, or watchdog timeout and host reboot) and possibly have unspecified other impact via unknown vectors.
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Analysis
by VulDB Data Team • 06/30/2022
The vulnerability identified as CVE-2015-8338 represents a critical security flaw in the Xen hypervisor affecting versions 4.6.x and earlier, specifically within the ARM architecture implementation. This issue stems from inadequate input validation mechanisms that fail to properly enforce limits on page order parameters within several memory management hypercalls. The affected hypercalls include XENMEM_increase_reservation, XENMEM_populate_physmap, and XENMEM_exchange, which are fundamental operations for managing memory allocation and reservation within virtualized environments. These suboperations form part of the core memory management interface between the hypervisor and guest operating systems, making them critical components for system stability and security.
The technical flaw manifests as a lack of proper boundary checking on page order inputs, which are used to specify the size and allocation parameters for memory regions. When malicious or malformed page order values are submitted through these hypercalls, the hypervisor fails to validate these inputs adequately, potentially allowing an attacker to manipulate memory allocation parameters beyond normal operational limits. This improper validation creates opportunities for resource exhaustion and system instability, as the hypervisor may attempt to process excessively large memory requests or perform operations that consume disproportionate system resources. The vulnerability falls under CWE-129, Input Validation and Representation, specifically addressing insufficient input bounds checking, and can be categorized under ATT&CK technique T1499.004 for Resource Exhaustion and T1068 for Exploitation for Privilege Escalation in virtualized environments.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise entire virtualized infrastructures. Guest OS administrators with sufficient privileges can exploit this weakness to cause significant system disruptions including CPU resource exhaustion, guest operating system reboots, or even host system reboots triggered by watchdog timeouts. The severity of these impacts depends on the specific implementation and system configuration, but the potential for cascading failures makes this vulnerability particularly dangerous in production environments. The unspecified other impacts mentioned in the description suggest that this vulnerability might also enable additional attack vectors or escalation paths that were not fully characterized during initial analysis. This type of vulnerability represents a classic case of insufficient input validation in hypervisor-level code, where the failure to properly validate user-supplied parameters creates opportunities for both intentional exploitation and accidental system instability.
Mitigation strategies for CVE-2015-8338 require immediate patching of affected Xen hypervisor versions to the latest stable releases that include proper input validation for page order parameters. Organizations should prioritize updating their hypervisor installations and implementing monitoring for anomalous memory allocation patterns that might indicate exploitation attempts. Additionally, system administrators should consider implementing strict resource limits and quotas for guest operating systems to reduce the potential impact of successful exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation in hypervisor code and underscores the need for comprehensive security testing of virtualization platforms, particularly in ARM-based environments where such issues may be more prevalent due to the complexity of memory management operations in these architectures.