CVE-2008-5136 in tkusr
Summary
by MITRE
tkusr in tkusr 0.82 allows local users to overwrite arbitrary files via a symlink attack on the /tmp/tkusr.pgm temporary file.
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Analysis
by VulDB Data Team • 10/14/2018
The vulnerability identified as CVE-2008-5136 resides within the tkusr 0.82 software package, specifically targeting the tkusr utility which is commonly used for managing user accounts and system configurations. This issue represents a classic insecure temporary file creation flaw that has significant implications for system security and privilege escalation. The vulnerability manifests when the tkusr utility creates temporary files without proper security measures, making it susceptible to symlink attacks that can be exploited by local users to overwrite arbitrary files on the system.
The technical flaw stems from the improper handling of temporary files within the tkusr utility's execution environment. When the utility operates, it creates a temporary file named tkusr.pgm in the /tmp directory without sufficient security checks or atomic creation mechanisms. This insecure practice allows local attackers to create symbolic links with the same name in the temporary directory before the utility can create its intended file. The vulnerability is classified as a race condition where the timing window between the symlink creation and the file creation provides an opportunity for malicious manipulation. This type of vulnerability is categorized under CWE-377 as "Insecure Temporary File" and aligns with CWE-378 which addresses "Creation of Temporary File With Insecure Permissions."
The operational impact of this vulnerability extends beyond simple file overwriting capabilities and can lead to privilege escalation and system compromise. A local attacker who successfully exploits this vulnerability can overwrite critical system files, configuration files, or even executable binaries with malicious content. This exploitation capability enables attackers to potentially gain elevated privileges or establish persistent access to the compromised system. The attack vector is particularly concerning because it requires minimal privileges and can be executed by any local user, making it a significant concern for system administrators who must maintain strict access controls and file permissions. The vulnerability also aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Python" and T1068 for "Exploitation for Privilege Escalation" when considering the broader attack chain that may be established through such file overwrites.
Mitigation strategies for this vulnerability should focus on immediate remediation through proper temporary file handling practices. System administrators should update to the latest version of tkusr that addresses this specific flaw, as the original version 0.82 contains the insecure implementation. Additionally, implementing proper file permissions and atomic file creation mechanisms can prevent similar vulnerabilities in other software components. The system should enforce strict temporary file creation practices where files are created with restrictive permissions and proper ownership. Security measures should include monitoring for unauthorized symbolic link creation in temporary directories and implementing proper privilege separation. Organizations should also consider implementing mandatory access controls and file integrity monitoring systems to detect and prevent unauthorized file modifications. The vulnerability serves as a reminder of the importance of secure coding practices and proper temporary file handling, which are fundamental requirements in secure software development lifecycle processes and align with industry standards such as those outlined in NIST SP 800-144 for secure programming practices.