Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Directory traversal vulnerability in clientarea.php in WHMCompleteSolution (WHMCS) 3.x.x allows remote attackers to read arbitrary files via an invalid action and a ../ (dot dot slash) in the templatefile parameter.
CWE-22 - Path Traversal
Path traversal (or directory traversal), is a vulnerability that allows malicious users to traverse the server's root directory, gaining access to arbitrary files and folders such as application code & data, back-end credentials, and sensitive operating system files. In the worst-case scenario, an attacker could potentially execute arbitrary files on the server, resulting in a denial of service attack. Such an exploit may severely impact the integrity, confidentiality, and availability of an application.