CVE-2011-5061 in WHMCompleteSolution
Summary
by MITRE
functions.php in WHMCompleteSolution (WHMCS) 4.0.x through 5.0.x allows remote attackers to trigger arbitrary code execution in the Smarty templating system by submitting a crafted ticket, related to improper handling of characters in the subject field.
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Analysis
by VulDB Data Team • 02/13/2019
The vulnerability CVE-2011-5061 represents a critical remote code execution flaw in WHMCompleteSolution (WHMCS) versions 4.0.x through 5.0.x that exploits improper input validation within the Smarty templating system. This vulnerability specifically targets the functions.php file which processes ticket submissions, creating a pathway for attackers to inject malicious code that gets executed within the web application's context. The attack vector involves crafting a malicious ticket subject field that contains specially formatted characters which, when processed by the Smarty template engine, trigger unintended code execution. This flaw operates at the intersection of input sanitization failures and template engine vulnerabilities, making it particularly dangerous as it allows attackers to execute arbitrary commands on the affected server. The vulnerability is classified under CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and aligns with ATT&CK technique T1190, "Exploit Public-Facing Application" and T1059, "Command and Scripting Interpreter."
The technical exploitation of this vulnerability occurs when the Smarty templating system processes user input from the ticket subject field without proper sanitization or escaping mechanisms. When an attacker submits a crafted subject line containing malicious template syntax or code injection payloads, the Smarty engine interprets these inputs as executable code rather than plain text. The vulnerability stems from insufficient validation of user-supplied data before it is passed to the template processing engine, allowing attackers to bypass normal input filtering mechanisms. This creates a scenario where legitimate template variables become vectors for malicious code execution, enabling attackers to perform operations such as file system manipulation, command execution, or data exfiltration. The impact is amplified because WHMCS is typically installed on web servers with elevated privileges, potentially allowing attackers to gain complete system compromise.
The operational impact of CVE-2011-5061 extends beyond simple code execution to encompass full system compromise and data breach potential. Attackers can leverage this vulnerability to establish persistent access, deploy backdoors, or extract sensitive customer information stored within WHMCS databases. The vulnerability affects organizations using hosting management platforms that rely on WHMCS for client ticketing and support operations, potentially exposing financial data, customer credentials, and system configurations. Organizations may experience service disruption, regulatory compliance violations, and significant financial losses due to data breaches or system compromise. The vulnerability's exploitation requires minimal technical skill, making it attractive to both automated attack tools and skilled adversaries. Security professionals must consider this vulnerability in the context of broader attack chains where initial access through web application exploits leads to lateral movement and persistent presence within target networks.
Mitigation strategies for CVE-2011-5061 require immediate patching of affected WHMCS versions to the latest secure releases that address the input sanitization issues. Organizations should implement strict input validation and sanitization measures for all user-supplied data, particularly in template processing contexts. Network-based mitigations include implementing web application firewalls to detect and block suspicious template syntax patterns in ticket subject fields. Regular security audits and penetration testing should verify that input handling mechanisms properly escape or sanitize template variables. Organizations should also implement monitoring solutions to detect unusual patterns in ticket submission activities that might indicate exploitation attempts. The vulnerability highlights the importance of secure coding practices and proper template engine configuration, emphasizing that developers must never trust user input and must always validate and sanitize all data before processing. Additionally, security teams should maintain updated threat intelligence feeds to identify potential exploitation attempts targeting this specific vulnerability and ensure that all systems receive timely security updates.