CVE-2008-3687 in Xen
Summary
by MITRE
Heap-based buffer overflow in the flask_security_label function in Xen 3.3, when compiled with the XSM:FLASK module, allows unprivileged domain users (domU) to execute arbitrary code via the flask_op hypercall.
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Analysis
by VulDB Data Team • 10/05/2018
The vulnerability described in CVE-2008-3687 represents a critical heap-based buffer overflow within the Xen hypervisor version 3.3 that specifically affects systems utilizing the XSM:FLASK security module. This flaw exists in the flask_security_label function, which is responsible for managing security labels within the hypervisor's security framework. The vulnerability arises from insufficient input validation when processing the flask_op hypercall, a mechanism that allows domain users to interact with the security labeling system. The flaw enables unprivileged domain users running in domU environments to exploit this vulnerability and execute arbitrary code with elevated privileges. The heap-based nature of the overflow indicates that the vulnerability occurs in dynamically allocated memory regions, making it particularly dangerous as it can lead to memory corruption that may be leveraged for privilege escalation attacks. This vulnerability directly impacts the fundamental security model of Xen hypervisors, potentially allowing malicious users to break out of their isolated domain environments and gain control over the host system or other domains.
The technical implementation of this vulnerability stems from improper bounds checking within the flask_security_label function when handling user-supplied data through the flask_op hypercall interface. When an unprivileged domain user submits crafted input to this hypercall, the system fails to validate the size or content of the data being processed, leading to a situation where more data is written to a heap-allocated buffer than it can accommodate. This buffer overflow condition creates opportunities for attackers to overwrite adjacent memory locations, potentially corrupting critical data structures or injecting malicious code that can be executed in the context of the privileged hypervisor. The vulnerability is particularly concerning because it operates within the XSM:FLASK module, which is designed to provide mandatory access control mechanisms that should prevent such privilege escalation scenarios. The flaw exists in the hypervisor's security subsystem rather than in user-space applications, meaning that successful exploitation could allow attackers to bypass the hypervisor's security controls and gain unauthorized access to system resources.
The operational impact of CVE-2008-3687 is severe and far-reaching for virtualized environments that rely on Xen hypervisors with XSM:FLASK enabled. An attacker with access to a domU environment could leverage this vulnerability to execute arbitrary code on the host system, effectively breaking the isolation between virtual machines and potentially compromising the entire virtualization infrastructure. This could result in complete system compromise, data theft, or the ability to launch further attacks against other virtual machines or the underlying physical hardware. The vulnerability essentially undermines the security model that virtualization platforms are designed to provide, allowing unprivileged users to escalate their privileges beyond the intended boundaries of their virtual domain. Organizations running Xen-based virtualization environments would face significant risk if they had not patched this vulnerability, as it could be exploited by attackers who gain access to any unprivileged domain within their virtual infrastructure. The attack vector is particularly dangerous because it requires minimal privileges to initiate, making it accessible to attackers who may only have basic user access within a virtual machine.
Mitigation strategies for CVE-2008-3687 primarily focus on patching the vulnerable Xen hypervisor version 3.3 with the appropriate security updates that address the buffer overflow in the flask_security_label function. Organizations should immediately upgrade to patched versions of Xen that contain fixes for this vulnerability, typically found in Xen 3.4 and subsequent releases. System administrators should also consider implementing additional security measures such as disabling the XSM:FLASK module if it is not essential for their security requirements, though this approach may reduce overall system security. Monitoring for suspicious hypercall activity and implementing intrusion detection systems that can identify potential exploitation attempts is recommended. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of how improper input validation in privileged code can lead to severe security consequences. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and could be categorized under T1068, which covers "Exploitation for Privilege Escalation," as the attack allows unprivileged users to gain elevated privileges within the virtualization environment. Regular security assessments and vulnerability scanning of virtualization environments are essential to identify and remediate similar issues that may exist in other components of the virtualization stack.