CVE-2015-7969 in Xen
Summary
by MITRE
Multiple memory leaks in Xen 4.0 through 4.6.x allow local guest administrators or domains with certain permission to cause a denial of service (memory consumption) via a large number of "teardowns" of domains with the vcpu pointer array allocated using the (1) XEN_DOMCTL_max_vcpus hypercall or the xenoprofile state vcpu pointer array allocated using the (2) XENOPROF_get_buffer or (3) XENOPROF_set_passive hypercall.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-7969 represents a critical memory management flaw in the Xen hypervisor affecting versions 4.0 through 4.6.x. This issue manifests as multiple memory leaks that occur during domain teardown operations, specifically when handling virtual cpu pointer arrays. The vulnerability operates at the hypervisor level and can be exploited by local guest administrators or domains with specific permissions, making it particularly concerning for multi-tenant cloud environments where guest isolation is paramount. The flaw stems from inadequate memory cleanup procedures during the termination of virtual machines, creating persistent memory allocations that cannot be properly released back to the system.
The technical implementation of this vulnerability involves two primary attack vectors that leverage different hypercall interfaces within the Xen hypervisor architecture. The first vector utilizes the XEN_DOMCTL_max_vcpus hypercall, which allows for the manipulation of virtual cpu configurations during domain lifecycle operations. The second vector targets the xenoprofile state vcpu pointer array through either the XENOPROF_get_buffer or XENOPROF_set_passive hypercalls, which are used for performance profiling and monitoring functions. Both attack paths result in memory leaks because the hypervisor fails to properly deallocate memory structures associated with virtual cpu pointer arrays when domains are torn down, leading to gradual memory exhaustion over time.
The operational impact of CVE-2015-7969 extends beyond simple denial of service conditions, as it can severely compromise system stability and resource availability. When exploited, the vulnerability allows attackers to consume increasing amounts of system memory through repeated domain teardown operations, eventually leading to system instability or complete resource exhaustion. This particular weakness aligns with CWE-401, which addresses memory leaks in software systems, and demonstrates how hypervisor-level memory management failures can cascade into broader system vulnerabilities. The attack requires only local access within a guest domain or specific permission levels, making it accessible to attackers who have already compromised a guest environment, which is a common scenario in cloud computing environments where guest isolation is not absolute.
This vulnerability directly relates to the ATT&CK framework's privilege escalation and resource exhaustion tactics, as it allows adversaries to consume system resources and potentially gain further access through system instability. The memory leaks occur during domain teardown operations, which are routine administrative functions, making the exploitation difficult to detect through normal monitoring systems. The vulnerability's impact is particularly severe in virtualized environments where multiple domains share the same physical host, as a single compromised guest domain can potentially affect the entire system's memory resources. Organizations should implement immediate mitigations including patching to affected Xen versions, monitoring for abnormal memory consumption patterns, and implementing strict access controls to limit guest domain privileges that could trigger these memory leaks. The vulnerability underscores the critical importance of proper memory management in hypervisor implementations and the potential for seemingly routine operations to become significant security risks when memory cleanup procedures are inadequate.