CVE-2013-4371 in Xen
Summary
by MITRE
Use-after-free vulnerability in the libxl_list_cpupool function in the libxl toolstack library in Xen 4.2.x and 4.3.x, when running "under memory pressure," returns the original pointer when the realloc function fails, which allows local users to cause a denial of service (heap corruption and crash) and possibly execute arbitrary code via unspecified vectors.
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Analysis
by VulDB Data Team • 05/26/2021
The CVE-2013-4371 vulnerability represents a critical use-after-free flaw within the Xen hypervisor's libxl toolstack library, specifically affecting versions 4.2.x and 4.3.x. This vulnerability manifests in the libxl_list_cpupool function where improper memory management occurs under specific conditions. The flaw occurs when the system operates under memory pressure, a common scenario in virtualized environments where resources are constrained and memory allocation becomes critical. The vulnerability stems from the library's handling of memory reallocation operations where the original pointer is returned even when the realloc function fails, creating a dangerous state where freed memory can be accessed and manipulated by subsequent operations.
The technical exploitation of this vulnerability involves a sophisticated understanding of heap management and memory allocation patterns within the Xen hypervisor environment. When memory pressure occurs during the execution of libxl_list_cpupool, the realloc function may fail to allocate additional memory, yet the code continues to reference the previously freed memory location. This creates a use-after-free condition that can be leveraged by local attackers to corrupt heap memory structures. The vulnerability operates at the intersection of memory management and process isolation, where the hypervisor's toolstack fails to properly validate memory allocation outcomes. This flaw aligns with CWE-416, which specifically addresses use-after-free vulnerabilities, and demonstrates how improper memory management can lead to system instability and potential code execution.
The operational impact of CVE-2013-4371 extends beyond simple denial of service to potentially enable arbitrary code execution within the hypervisor environment. Under memory pressure conditions, local users can trigger heap corruption that may lead to crashes or more severe consequences depending on the specific memory layout and exploitation vectors available. The vulnerability affects the stability of virtualized environments where Xen serves as the hypervisor, potentially compromising the integrity of multiple virtual machines running on the same host. Attackers can exploit this weakness to cause system-wide crashes, leading to denial of service for all virtualized workloads, or potentially escalate privileges to execute malicious code with the privileges of the hypervisor process. This vulnerability particularly impacts cloud computing environments and server virtualization platforms where resource constraints are common and memory management efficiency is critical.
Mitigation strategies for CVE-2013-4371 should focus on immediate patching of affected Xen versions, implementing memory pressure monitoring, and applying defensive programming practices within the toolstack. Organizations should prioritize upgrading to patched versions of Xen 4.2.x and 4.3.x, as the vulnerability was addressed in subsequent releases through improved memory management in the libxl library. System administrators should implement monitoring solutions that detect memory pressure conditions and automatically trigger defensive measures. The vulnerability demonstrates the importance of proper error handling in memory allocation operations and aligns with ATT&CK technique T1059 for execution through hypervisor manipulation. Additional protective measures include implementing strict memory limits for virtual machines, using memory-safe programming languages for critical components, and conducting regular security audits of hypervisor toolstacks to identify similar memory management flaws that could lead to similar vulnerabilities.