CVE-2018-5520 in BIG-IP
Summary
by MITRE
On an F5 BIG-IP 13.0.0-13.1.0.5, 12.1.0-12.1.3.1, or 11.2.1-11.6.3.1 system configured in Appliance mode, the TMOS Shell (tmsh) may allow an administrative user to use the dig utility to gain unauthorized access to file system resources.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2018-5520 represents a critical privilege escalation and information disclosure flaw within F5 BIG-IP systems operating in appliance mode. This vulnerability affects multiple versions of the F5 BIG-IP platform including 13.0.0 through 13.1.0.5, 12.1.0 through 12.1.3.1, and 11.2.1 through 11.6.3.1 releases. The flaw specifically resides within the TMOS Shell (tmsh) component which serves as the command-line interface for managing BIG-IP systems. When an administrative user executes the dig utility through this interface, the system fails to properly validate file system access permissions, creating a pathway for unauthorized file system traversal and access to sensitive system resources.
The technical exploitation of this vulnerability stems from improper input validation within the tmsh command processing mechanism. The dig utility, which is typically used for DNS resolution queries, is being leveraged to bypass normal file system access controls when executed through the TMOS Shell interface. This occurs because the system does not adequately sanitize or restrict the parameters passed to the underlying dig command, allowing an attacker with administrative privileges to craft malicious commands that can access files outside of the intended scope. This behavior aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal vulnerabilities. The flaw essentially allows an attacker to exploit the legitimate dig functionality to perform unauthorized file system operations.
The operational impact of this vulnerability is severe and multifaceted, potentially enabling attackers to access sensitive system files, configuration data, and potentially credentials stored within the BIG-IP appliance. An attacker who gains administrative access through this vulnerability could extract critical system information including SSL certificates, configuration files, user credentials, and other sensitive data that could be used for further exploitation. The vulnerability could also enable lateral movement within network infrastructure if the BIG-IP system serves as a central point for network traffic management. This access could facilitate more sophisticated attacks such as man-in-the-middle operations or complete network compromise. According to ATT&CK framework, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1078 (Valid Accounts) as it allows for privilege escalation and unauthorized access to system resources through legitimate administrative interfaces.
Mitigation strategies for CVE-2018-5520 should focus on immediate patching of affected systems with the vendor-provided security updates. Organizations must ensure all BIG-IP systems are updated to versions that address this specific vulnerability, as F5 released patches specifically targeting this flaw. Network segmentation and access control measures should be implemented to limit administrative access to only necessary personnel, reducing the attack surface. Regular monitoring of system logs for suspicious tmsh command usage and unusual file access patterns should be established. Additionally, implementing principle of least privilege for administrative accounts and disabling unnecessary services such as the dig utility when not required can help reduce the risk exposure. Security teams should also conduct thorough vulnerability assessments to identify any other potential path traversal or privilege escalation vulnerabilities within their BIG-IP deployments and related infrastructure components.