CVE-2008-4993 in Xen
Summary
by MITRE
qemu-dm.debug in Xen 3.2.1 allows local users to overwrite arbitrary files via a symlink attack on the /tmp/args temporary file.
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Analysis
by VulDB Data Team • 08/23/2019
The vulnerability identified as CVE-2008-4993 affects the qemu-dm.debug component within the Xen 3.2.1 virtualization platform, presenting a significant security risk through a symlink attack vector. This flaw exists within the temporary file handling mechanism of the Xen hypervisor's disk management subsystem, specifically targeting the /tmp/args file that serves as a temporary storage location for command-line arguments during virtual machine operations. The vulnerability stems from insufficient validation of temporary file creation processes, allowing local authenticated attackers to manipulate the system's file creation behavior through symbolic link manipulation.
The technical implementation of this vulnerability exploits a race condition in the temporary file creation sequence where the qemu-dm.debug utility creates temporary files without proper security checks. When the utility attempts to create the /tmp/args file, it does not verify whether the target path already exists as a symbolic link, enabling attackers to pre-create symbolic links that point to critical system files or configuration locations. This creates a scenario where file operations intended for the temporary file actually modify the targeted symbolic link destination, potentially overwriting important system files or configuration data with attacker-controlled content. The flaw aligns with CWE-377, which addresses insecure temporary file handling, and represents a classic example of a race condition vulnerability that has been documented in numerous security advisories.
The operational impact of this vulnerability extends beyond simple file overwrites, as it provides attackers with persistent access to modify critical system components through the compromised virtualization layer. Local users with access to the Xen environment can leverage this weakness to escalate privileges, modify system configuration files, or potentially inject malicious code into the virtualization infrastructure. The attack vector is particularly concerning because it operates at the hypervisor level, meaning successful exploitation could compromise the entire virtualization environment and affect multiple virtual machines running on the same host. This vulnerability also aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, and T1068, which addresses local privilege escalation through race conditions.
Mitigation strategies for CVE-2008-4993 require immediate implementation of proper temporary file handling procedures within the Xen hypervisor components. System administrators should ensure that all temporary file creation operations include proper validation checks to prevent symbolic link attacks, specifically implementing checks for existing file paths before creating temporary files. The recommended approach involves using secure temporary file creation methods that employ atomic operations or proper file permission controls to prevent attackers from creating symbolic links in the target directory. Additionally, organizations should consider implementing mandatory access controls and privilege separation mechanisms to limit the impact of such vulnerabilities, while also ensuring that all Xen hypervisor components are updated to versions that have addressed this specific race condition. Regular security audits and monitoring of temporary file creation patterns should be implemented to detect potential exploitation attempts.