CVE-2013-1964 in Xen
Summary
by MITRE
Xen 4.0.x and 4.1.x incorrectly releases a grant reference when releasing a non-v1, non-transitive grant, which allows local guest administrators to cause a denial of service (host crash), obtain sensitive information, or possible have other impacts via unspecified vectors.
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Analysis
by VulDB Data Team • 05/10/2021
The vulnerability identified as CVE-2013-1964 affects the Xen hypervisor versions 4.0.x and 4.1.x, representing a critical flaw in the grant reference management system that governs memory sharing between guest operating systems and the host hypervisor. This issue stems from improper handling of grant references within the Xen virtualization environment, specifically when dealing with non-v1, non-transitive grant entries. The flaw exists at the core of Xen's memory management subsystem where grant references are used to establish secure memory mappings between domains. When a guest administrator attempts to release such grant references, the hypervisor fails to properly decrement the reference count, leading to a state where the reference remains in an inconsistent condition.
The technical implementation of this vulnerability involves the grant table management within Xen's hypervisor layer, where each grant entry maintains a reference count to track how many domains are actively using that memory mapping. The flaw manifests when the hypervisor processes grant references that do not conform to the v1 or transitive grant formats, which are typically used for specific memory sharing patterns. This improper reference handling creates a condition where the grant reference can be released twice or not released at all, causing memory corruption within the hypervisor's internal data structures. The vulnerability allows for a range of potential impacts including system crashes, information disclosure, and potentially privilege escalation.
From an operational perspective, this vulnerability presents a significant risk to virtualized environments as it can be exploited by local guest administrators who possess administrative privileges within their virtual machine. The impact extends beyond simple denial of service to potentially allow for information disclosure attacks where sensitive data from the host system or other guest domains could be accessed. The unspecified vectors mentioned in the description suggest that the exploitation may occur through various means including memory manipulation, process scheduling interference, or direct manipulation of grant table entries. This vulnerability directly relates to CWE-121 and CWE-125 which address buffer overflow conditions and out-of-bounds read/write errors, and aligns with ATT&CK technique T1059 for command and scripting interpreter and T1499 for endpoint denial of service.
The mitigation strategies for this vulnerability require immediate patching of Xen hypervisor installations to versions 4.2.0 and later, which contain the necessary fixes for proper grant reference management. Organizations should also implement monitoring for unusual memory access patterns and grant table modifications within their virtualized environments. Security teams should consider implementing domain isolation measures and restricting guest administrator privileges where possible. Additionally, regular vulnerability assessments of virtualization infrastructure should be conducted to identify similar issues in other hypervisor components. The fix implemented by Xen developers addresses the core reference counting logic to ensure proper decrementing of grant references and prevents the double-release condition that was exploited in this vulnerability, thereby restoring the integrity of the hypervisor's memory management system and protecting against the potential for host-level compromise.