CVE-2012-6031 in Xen
Summary
by MITRE
The do_tmem_get function in the Transcendent Memory (TMEM) in Xen 4.0, 4.1, and 4.2 allow local guest OS users to cause a denial of service (CPU hang and host crash) via unspecified vectors related to a spinlock being held in the "bad_copy error path." NOTE: this issue was originally published as part of CVE-2012-3497, which was too general; CVE-2012-3497 has been SPLIT into this ID and others.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2012-6031 resides within the Transcendent Memory (TMEM) subsystem of the Xen hypervisor version 4.0, 4.1, and 4.2, representing a critical security flaw that enables local guest operating system users to execute denial of service attacks against the host system. This vulnerability specifically affects the do_tmem_get function which handles memory operations within the TMEM framework, creating a scenario where malicious guest users can manipulate the system's behavior through improper handling of spinlock states during error conditions. The issue stems from the improper management of spinlocks within the error handling path of the TMEM subsystem, where a spinlock remains held during what should be a clean error recovery process, leading to system-wide operational failure.
The technical flaw manifests when a guest OS user triggers the bad_copy error path within the TMEM implementation, causing the system to enter an indefinite spinlock hold state. This condition occurs because the spinlock mechanism, designed to prevent concurrent access to shared resources, fails to release properly when an error occurs during memory copy operations. The spinlock being held indefinitely prevents other threads or processes from accessing the protected resources, effectively creating a deadlock condition that can result in complete CPU hang or system crash. This represents a classic example of improper resource management where the error handling code path does not properly clean up acquired locks, leading to system instability. The vulnerability falls under CWE-667, which addresses improper locking mechanisms, and aligns with ATT&CK technique T1499.004 related to network denial of service attacks through hypervisor manipulation.
The operational impact of this vulnerability extends beyond simple denial of service, as it can result in complete system compromise when exploited by malicious guest users. Host crashes and CPU hangs can lead to complete system downtime, affecting all virtual machines running on the compromised hypervisor. Since this vulnerability exists within the hypervisor layer, it provides attackers with a powerful means of disrupting services across multiple guest operating systems, potentially affecting critical infrastructure operations. The issue is particularly dangerous because it requires only local access within a guest OS to exploit, making it accessible to users who may not have elevated privileges. This vulnerability demonstrates how hypervisor-level flaws can create cascading effects that compromise the entire virtualization environment, as the affected spinlock state can propagate throughout the system's memory management subsystem.
Mitigation strategies for CVE-2012-6031 should focus on immediate patch application to Xen hypervisor versions 4.0, 4.1, and 4.2, as the vulnerability has been addressed through proper spinlock handling in updated releases. System administrators should implement monitoring for unusual CPU utilization patterns that might indicate spinlock contention issues, particularly in environments where multiple guest VMs are running. The fix involves ensuring that error paths properly release spinlocks before terminating execution, preventing the indefinite hold that causes system instability. Additionally, implementing proper resource isolation and access controls within virtual environments can help limit the potential impact of such vulnerabilities. Organizations should also consider implementing hypervisor hardening measures, including disabling unnecessary TMEM functionality when not required, and maintaining regular security assessments of virtualization environments to identify similar resource management flaws that could lead to system-wide failures. The vulnerability highlights the importance of thorough error handling in hypervisor code and the need for comprehensive testing of all code paths, particularly those involving shared resource management and locking mechanisms.