CVE-2008-5716 in xen
Summary
by MITRE
xend in Xen 3.3.0 does not properly restrict a guest VM s write access within the /local/domain xenstore directory tree, which allows guest OS users to cause a denial of service and possibly have unspecified other impact by writing to (1) console/tty, (2) console/limit, or (3) image/device-model-pid. NOTE: this issue exists because of erroneous set_permissions calls in the fix for CVE-2008-4405.
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Analysis
by VulDB Data Team • 10/22/2018
The vulnerability identified as CVE-2008-5716 represents a critical access control flaw within the Xen hypervisor version 3.3.0, specifically affecting the xend management daemon. This issue stems from improper permission restrictions within the xenstore directory tree, which serves as the primary communication channel between hypervisor components and guest virtual machines. The vulnerability manifests when guest operating systems are granted excessive write privileges to critical xenstore paths that should remain restricted to hypervisor-level operations. The flaw particularly affects three sensitive paths: console/tty, console/limit, and image/device-model-pid, all of which are crucial for maintaining system stability and security boundaries between virtualized environments.
The technical root cause of this vulnerability lies in erroneous set_permissions calls that were implemented as part of the fix for CVE-2008-4405, creating a regression that inadvertently weakened access controls. This demonstrates how security patches, when improperly implemented, can introduce new vulnerabilities rather than resolving existing ones. The xenstore directory structure provides a hierarchical namespace for hypervisor-guest communication, where each node represents a specific configuration or operational parameter. When guest VMs can write to these restricted paths, they gain the ability to manipulate fundamental system behaviors that should remain under hypervisor control. The console/tty path allows modification of console output handling, console/limit controls output rate limiting, and image/device-model-pid manages the process identifier of the device model, all of which can be exploited to disrupt normal system operations.
The operational impact of this vulnerability extends beyond simple denial of service conditions, potentially enabling arbitrary code execution or complete system compromise depending on the specific exploitation vector. Attackers can leverage this flaw to disrupt console functionality, limit output streams to prevent diagnostic information from being displayed, or manipulate device model processes to cause system instability. From an attacker perspective, this represents a privilege escalation opportunity that can be used to gain deeper control over the virtualized environment, potentially allowing access to other VMs or the host system itself. The vulnerability is particularly concerning because it operates at the hypervisor level, meaning that successful exploitation can affect all virtual machines running on the compromised host, creating a potential attack surface that spans multiple isolated environments.
Security researchers have classified this vulnerability according to CWE-276, which addresses improper permissions and access control, making it a prime example of how inadequate access control mechanisms can create persistent security risks. The vulnerability also maps to several ATT&CK techniques including privilege escalation through access token manipulation and defense evasion by disrupting system logging and monitoring capabilities. Organizations running Xen hypervisor versions 3.3.0 should prioritize immediate remediation through patching, as this vulnerability represents a significant risk to virtualized environments. The recommended mitigation strategy involves upgrading to a patched version of Xen hypervisor where proper access controls have been re-established for the xenstore directory tree. Additionally, implementing network segmentation and monitoring for unusual xenstore access patterns can provide additional defensive layers, though these measures are secondary to the core patching requirement. This vulnerability underscores the critical importance of thorough testing and validation of security patches, particularly when addressing complex hypervisor-level access control mechanisms that govern the fundamental security boundaries of virtualized computing environments.