CVE-2015-7814 in Xen
Summary
by MITRE
Race condition in the relinquish_memory function in arch/arm/domain.c in Xen 4.6.x and earlier allows local domains with partial management control to cause a denial of service (host crash) via vectors involving the destruction of a domain and using XENMEM_decrease_reservation to reduce the memory of the domain.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-7814 represents a critical race condition within the Xen hypervisor's memory management subsystem, specifically affecting versions 4.6.x and earlier. This flaw exists in the relinquish_memory function located in arch/arm/domain.c, which governs how virtual machines handle memory allocation and deallocation within the hypervisor environment. The vulnerability arises from improper synchronization mechanisms during domain destruction processes, creating a window where concurrent operations can lead to unpredictable system behavior.
The technical implementation of this vulnerability exploits a timing issue where local domains with partial management privileges can manipulate memory reservation operations in a manner that triggers the race condition. When a domain is being destroyed and the XENMEM_decrease_reservation operation is simultaneously executed, the memory management subsystem fails to properly coordinate these competing operations. This race condition specifically affects ARM-based Xen deployments and occurs because the relinquish_memory function does not adequately protect against concurrent access patterns that can lead to memory corruption or invalid pointer dereferences. The flaw essentially allows an attacker to manipulate the timing of memory management operations to cause the hypervisor to execute invalid memory operations that result in system crashes.
The operational impact of CVE-2015-7814 extends beyond simple denial of service, as it can lead to complete system compromise when exploited by malicious local users who have partial management control over domains. This vulnerability falls under CWE-362, which specifically addresses race conditions in software systems, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The exploitability requires local access with partial management privileges, making it particularly dangerous in multi-tenant environments where users might have legitimate but limited administrative rights. When successfully exploited, the vulnerability can cause the entire host system to crash, effectively creating a denial of service condition that impacts all virtual machines running on that hypervisor.
Mitigation strategies for CVE-2015-7814 primarily involve upgrading to Xen versions 4.7.0 and later, where the race condition has been addressed through improved synchronization mechanisms in the memory management subsystem. System administrators should implement strict access controls to limit local domain privileges and ensure that only trusted users have partial management capabilities. Additionally, monitoring for unusual memory reservation patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The fix implemented in later Xen versions addresses the root cause by introducing proper locking mechanisms and ensuring that memory management operations during domain destruction are properly serialized to prevent concurrent access issues. Organizations should also consider implementing virtualization security frameworks that provide additional layers of protection against such timing-based vulnerabilities in hypervisor environments.