CVE-2007-3919 in xen
Summary
by MITRE
(1) xenbaked and (2) xenmon.py in Xen 3.1 and earlier allow local users to truncate arbitrary files via a symlink attack on /tmp/xenq-shm.
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Analysis
by VulDB Data Team • 07/29/2019
The vulnerability described in CVE-2007-3919 represents a critical security flaw affecting Xen hypervisor versions 3.1 and earlier. This issue manifests through two distinct components xenbaked and xenmon.py which together create a pathway for local privilege escalation through file system manipulation. The vulnerability specifically targets the temporary file handling mechanism within the Xen virtualization environment, where these tools create and manage shared memory segments in the /tmp directory. The flaw exploits the insecure creation of temporary files without proper atomic operations, creating a window of opportunity for malicious users to exploit the system through symbolic link attacks.
The technical implementation of this vulnerability stems from the insecure temporary file creation practices employed by the xenbaked and xenmon.py utilities. When these components execute, they create temporary files in the /tmp/xenq-shm location without sufficient security controls to prevent symbolic link manipulation. An attacker can leverage this weakness by creating a symbolic link with the same name as the target file, effectively redirecting the write operations intended for legitimate files to arbitrary locations on the file system. This technique falls under the category of race condition vulnerabilities and represents a classic example of insecure temporary file handling as defined by CWE-377. The vulnerability enables local users to perform file truncation attacks against arbitrary files on the system, potentially compromising system integrity and confidentiality.
The operational impact of CVE-2007-3919 extends beyond simple file manipulation, as it provides attackers with the capability to overwrite critical system files or configuration data. This vulnerability is particularly dangerous in virtualized environments where the hypervisor controls multiple guest operating systems, as successful exploitation could lead to privilege escalation and potentially full system compromise. The attack vector requires local access to the system, but once executed, it can be leveraged to modify system files that would normally require higher privileges. The vulnerability is particularly concerning from an attack surface perspective as it operates within the legitimate hypervisor processes, making detection more difficult. This aligns with ATT&CK technique T1055 for privilege escalation through exploitation of legitimate system processes.
Mitigation strategies for this vulnerability involve immediate patching of affected Xen hypervisor versions to address the insecure temporary file handling mechanisms. System administrators should ensure that all Xen installations are updated to versions that properly implement atomic file creation operations and validate temporary file paths before use. Additionally, the affected utilities should be configured to run with restricted permissions and in secure temporary directories that cannot be manipulated by unprivileged users. The implementation of proper file system permissions and access controls can significantly reduce the attack surface for this vulnerability. Organizations should also consider implementing monitoring solutions to detect suspicious file system activity and symbolic link creation patterns that may indicate exploitation attempts. The fix typically involves modifying the temporary file creation logic to use secure methods such as O_CREAT | O_EXCL flags or proper atomic operations to prevent the race condition that enables this attack.