CVE-2018-17835 in GetSimple
Summary
by MITRE
An issue was discovered in GetSimple CMS 3.3.15. An administrator can insert stored XSS via the admin/settings.php Custom Permalink Structure parameter, which injects the XSS payload into any page created at the admin/pages.php URI.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/19/2023
This vulnerability exists within GetSimple CMS version 3.3.15 where an authenticated administrator can exploit a stored cross-site scripting flaw through the settings.php page. The vulnerability specifically targets the Custom Permalink Structure parameter which allows arbitrary code injection that persists in the application's configuration. When an administrator modifies this setting, the input validation is insufficient to prevent malicious payloads from being stored and subsequently executed whenever pages are rendered through the pages.php URI. This creates a persistent threat vector where any user visiting affected pages could be compromised without any additional interaction from the victim.
The technical flaw represents a classic stored XSS vulnerability that operates through the application's administrative interface. The vulnerability stems from inadequate input sanitization and output encoding mechanisms within the CMS's configuration handling system. When the administrator saves the Custom Permalink Structure setting, the application fails to properly validate or escape the input before storing it in the system configuration. This allows malicious payloads to be injected and stored in the database or configuration files, where they remain dormant until accessed by the vulnerable pages.php endpoint. The attack chain begins with administrative access and leverages the trust relationship between the application and its administrator to establish a persistent XSS vector.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking. An attacker with administrative privileges can execute arbitrary JavaScript code in the context of other users' browsers, potentially leading to complete system compromise. The stored nature of the vulnerability means that the attack persists even after the initial injection, making it particularly dangerous for long-term exploitation. The vulnerability affects all users who visit pages created through the affected permalink structure, potentially compromising a wide user base. Additionally, the persistence of the vulnerability means that it remains active until the malicious payload is manually removed from the configuration, creating a continuous threat vector that can be exploited by any user with access to the affected pages.
Mitigation strategies should focus on immediate input validation and output encoding improvements within the CMS. The primary fix involves implementing strict input sanitization for all administrative settings, particularly those that affect URL structures or page rendering. The application should escape all user-provided content before storing it and ensure proper HTML escaping when rendering URLs or permalinks. Organizations should also implement principle of least privilege by limiting administrative access to trusted personnel and monitoring administrative activities for suspicious behavior. Regular security audits of CMS configurations and input validation mechanisms should be conducted to identify similar vulnerabilities. This vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws and represents a common pattern identified in the ATT&CK framework under T1059.007 for script injection techniques. The persistence of stored XSS vulnerabilities makes them particularly attractive to attackers, as they can maintain access over extended periods without requiring repeated exploitation attempts.