CVE-2018-11642 in PowerMedia XMS
Summary
by MITRE
Incorrect Permission Assignment on the /var/www/xms/cleanzip.sh shell script run periodically in Dialogic PowerMedia XMS through 3.5 allows local users to execute code as the root user.
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Analysis
by VulDB Data Team • 02/24/2020
The vulnerability identified as CVE-2018-11642 represents a critical privilege escalation flaw within Dialogic PowerMedia XMS version 3.5 and earlier systems. This issue stems from improper permission assignment on the /var/www/xms/cleanzip.sh shell script, which operates on a periodic basis within the system's cron scheduler. The vulnerability resides in the web application's directory structure where the cleanzip.sh script lacks appropriate access controls, creating a path for local attackers to gain elevated privileges. The script's execution context operates with root privileges, making it a prime target for malicious exploitation. This misconfiguration allows unauthorized local users to manipulate the script's behavior and ultimately execute arbitrary code with administrative privileges, effectively compromising the entire system's integrity.
The technical implementation of this vulnerability demonstrates a classic case of insecure file permissions combined with scheduled execution. The cleanzip.sh script, located in the web root directory structure, operates with root privileges due to its placement within the web application's execution path. When the script runs periodically through cron jobs, any local user with write access to the script or its parent directories can modify its contents to include malicious commands. This flaw aligns with CWE-276, which specifically addresses incorrect permission assignment, and represents a direct violation of the principle of least privilege. The vulnerability operates at the operating system level rather than through network-based attacks, making it particularly dangerous as it requires no external network access or authentication.
The operational impact of this vulnerability extends far beyond simple privilege escalation, creating a complete system compromise scenario for attackers. Local users who can access the system through legitimate means can leverage this flaw to execute commands as root, potentially leading to full system takeover, data exfiltration, or persistent backdoor installation. The periodic execution nature of the script means that the vulnerability remains exploitable over time, providing attackers with sustained access rather than a one-time opportunity. This type of vulnerability is particularly concerning in enterprise environments where multiple users may have legitimate local access to systems running Dialogic PowerMedia XMS. The attack vector falls under ATT&CK technique T1068, which covers local privilege escalation, and demonstrates how misconfigured permissions can create persistent security weaknesses.
Mitigation strategies for CVE-2018-11642 should focus on immediate permission correction and long-term system hardening. The primary fix involves setting proper file permissions on the cleanzip.sh script and its parent directories, ensuring that only authorized users or processes can modify the script contents. The recommended permissions should restrict write access to the root user only, while read and execute permissions should be appropriately limited. Additionally, implementing proper input validation and sanitization within the script itself can prevent command injection attacks. System administrators should also consider removing or disabling unnecessary cron jobs and regularly audit file permissions across the system. The remediation process should align with security frameworks such as NIST SP 800-53 controls, particularly those addressing access control and system configuration management. Regular security assessments and privilege reviews should be implemented to prevent similar misconfigurations from occurring in other system components.