CVE-2012-2625 in Xen
Summary
by MITRE
The PyGrub boot loader in Xen unstable before changeset 25589:60f09d1ab1fe, 4.2.x, and 4.1.x allows local para-virtualized guest users to cause a denial of service (memory consumption) via a large (1) bzip2 or (2) lzma compressed kernel image.
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Analysis
by VulDB Data Team • 12/19/2021
The vulnerability identified as CVE-2012-2625 affects the PyGrub boot loader component within the Xen hypervisor ecosystem, specifically impacting versions prior to critical changeset 25589:60f09d1ab1fe in the unstable branch as well as the 4.2.x and 4.1.x release lines. This issue represents a significant security concern within virtualized environments where para-virtualized guest operating systems are employed, as it enables malicious local users to exploit memory consumption patterns that can lead to system instability and resource exhaustion. The vulnerability manifests through the handling of compressed kernel images, specifically when bzip2 or lzma compression formats are utilized, creating a scenario where legitimate system operations can be disrupted through resource manipulation.
The technical flaw lies in the insufficient input validation and resource management within PyGrub's decompression routines. When a para-virtualized guest user presents a kernel image compressed with bzip2 or lzma formats, the boot loader processes these files without adequate safeguards against maliciously crafted compression data. The vulnerability stems from the lack of proper bounds checking and memory allocation limits during the decompression process, allowing an attacker to craft compressed kernel images that, when processed, consume excessive memory resources. This design weakness creates a path where the decompression algorithm can be forced into memory exhaustion conditions through carefully constructed compressed data that appears legitimate but triggers resource allocation patterns beyond normal operational parameters.
The operational impact of this vulnerability extends beyond simple denial of service conditions, potentially affecting the stability and performance of entire virtualized environments. Local users within para-virtualized guest systems can exploit this weakness to consume available memory resources on the host system, leading to cascading effects that may impact other virtual machines sharing the same physical hardware. The memory consumption can be so severe that it causes the hypervisor to become unresponsive or forces the system to terminate legitimate processes in order to maintain operational stability. This vulnerability is particularly concerning in multi-tenant cloud environments where guest isolation is paramount, as it could potentially allow one guest to affect the performance and availability of other guests on the same host system.
Mitigation strategies for this vulnerability require immediate patch application to the affected Xen hypervisor versions, with administrators prioritizing updates to the unstable branch to changeset 25589:60f09d1ab1fe or equivalent fixes in the 4.2.x and 4.1.x release lines. System administrators should implement monitoring solutions to detect unusual memory consumption patterns that might indicate exploitation attempts, particularly focusing on virtualization-related processes and memory allocation behaviors. Additional protective measures include implementing resource quotas and limits for virtual machine memory usage, deploying intrusion detection systems that can identify suspicious compressed data patterns, and conducting regular security audits of virtualization environments to ensure proper isolation between guest systems. The vulnerability aligns with CWE-400, which addresses unchecked resource allocation, and represents a specific implementation of resource exhaustion attacks that can be categorized under ATT&CK technique T1499.001 for network denial of service and T1059.001 for command and scripting interpreter usage patterns that may be leveraged in exploitation scenarios.
This vulnerability demonstrates the critical importance of proper resource management in hypervisor components and highlights the need for comprehensive security testing of virtualization infrastructure. The issue serves as a reminder that even components designed for legitimate system boot operations can become attack vectors when proper input validation and resource allocation controls are not implemented. Organizations should consider implementing additional security controls such as kernel module signing, virtual machine introspection capabilities, and regular penetration testing of their virtualization environments to identify similar weaknesses that could be exploited in similar fashion. The remediation process should include thorough testing of patched environments to ensure that the fix does not introduce compatibility issues with existing virtual machine configurations while maintaining the security posture against this specific resource exhaustion vulnerability.