CVE-2019-9971 in Phone System
Summary
by MITRE • 06/07/2022
PhoneSystem Terminal in 3CX Phone System (Debian based installation) 16.0.0.1570 allows an attacker to gain root privileges by using sudo with the tcpdump command, without a password. This occurs because the -z (aka postrotate-command) option to tcpdump can be unsafe when used in conjunction with sudo.
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Analysis
by VulDB Data Team • 06/10/2022
The vulnerability identified as CVE-2019-9971 affects the 3CX Phone System version 16.0.0.1570 running on Debian-based installations and represents a critical privilege escalation flaw that allows attackers to obtain root access through improper sudo configuration. This issue stems from the insecure use of the tcpdump command with the -z option within a sudo context, creating a dangerous attack vector that bypasses normal authentication mechanisms. The vulnerability specifically targets the PhoneSystem Terminal component where the sudoers configuration permits execution of tcpdump with elevated privileges without requiring password authentication, making it particularly dangerous for systems that rely on this service for telecommunications operations.
The technical flaw resides in how the sudo command handles the tcpdump utility when invoked with the -z parameter, which specifies a command to execute after log rotation. When an attacker can manipulate the tcpdump execution through sudo without password verification, they can leverage this to execute arbitrary commands with root privileges. The -z option in tcpdump is designed to execute a shell command after a log file is rotated, but when combined with sudo permissions, it creates a path for command injection that can be exploited to gain complete system control. This configuration violates the principle of least privilege and creates an attack surface where malicious users can escalate their privileges from regular user level to root access simply by manipulating the tcpdump execution context.
The operational impact of this vulnerability extends beyond simple privilege escalation as it affects the integrity and confidentiality of entire telecommunications infrastructure. Organizations using 3CX Phone System versions 16.0.0.1570 are at risk of complete system compromise, allowing attackers to access sensitive communication data, modify system configurations, install persistent backdoors, and potentially disrupt critical business communications. The vulnerability is particularly concerning in enterprise environments where phone systems handle confidential business communications and where attackers could exploit this to gain access to internal networks through the compromised phone system. This flaw directly relates to CWE-276 which addresses incorrect permissions for critical resources, and can be mapped to ATT&CK technique T1068 which involves exploiting vulnerabilities to gain system privileges.
Mitigation strategies for CVE-2019-9971 require immediate action to correct the sudoers configuration and restrict the tcpdump command execution privileges. System administrators should modify the sudoers file to remove or restrict the specific tcpdump command execution permissions that allow passwordless root access. The recommended approach involves either removing the sudo permission for tcpdump entirely if not required for legitimate operations, or implementing more restrictive command execution policies that prevent arbitrary command execution through the -z parameter. Additionally, organizations should implement regular security audits of sudo configurations and apply the official 3CX patch releases that address this specific vulnerability. Network segmentation and monitoring of tcpdump processes should also be implemented to detect potential exploitation attempts. The fix aligns with security best practices outlined in NIST SP 800-53 and ISO 27001 controls for privilege management and access control, ensuring that systems maintain proper segregation of duties and minimal privilege principles to prevent unauthorized escalation of privileges.