CVE-2016-8870 in Joomla
Summary
by MITRE
The register method in the UsersModelRegistration class in controllers/user.php in the Users component in Joomla! before 3.6.4, when registration has been disabled, allows remote attackers to create user accounts by leveraging failure to check the Allow User Registration configuration setting.
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Analysis
by VulDB Data Team • 02/01/2025
The vulnerability described in CVE-2016-8870 represents a critical access control flaw in the Joomla versions prior to 3.6.4. The vulnerability stems from a failure in the registration process validation logic where the system does not properly verify whether user registration has been explicitly disabled by the administrator. When registration is disabled through the configuration settings, the system should prevent any new user account creation attempts, but this check is bypassed in the affected versions, allowing unauthorized account creation through the register method.
The technical implementation of this vulnerability exploits a fundamental flaw in the application's input validation and access control mechanisms. The register method in the UsersModelRegistration class fails to reference the Allow User Registration configuration setting that administrators can set through the Joomla! backend interface. This misconfiguration allows remote attackers to submit registration requests regardless of the system's registration policy, effectively circumventing the intended security controls. The vulnerability is particularly dangerous because it operates at the application layer and requires no privileged access or authentication to exploit, making it highly accessible to attackers. According to CWE-650, this represents a weakness in the design of access control mechanisms where the system fails to properly validate user permissions before executing privileged operations.
From an operational perspective, this vulnerability creates significant security implications for Joomla! installations where user registration has been disabled for security reasons. Attackers can exploit this flaw to create unauthorized user accounts, potentially gaining access to restricted areas of the website or performing malicious activities such as spamming, content manipulation, or credential stuffing attacks. The impact extends beyond simple account creation as it undermines the entire user management framework and can lead to privilege escalation scenarios when combined with other vulnerabilities. This vulnerability aligns with ATT&CK technique T1133 which describes External Remote Services and demonstrates how attackers can leverage misconfigured access controls to establish unauthorized presence within a system.
The remediation strategy for this vulnerability requires immediate application of the official Joomla installations to ensure no other similar access control bypasses exist within the system. System administrators must verify that all configuration settings are properly enforced and that the application performs adequate input validation before executing user creation operations. Additionally, implementing network-level monitoring and intrusion detection systems can help identify unauthorized registration attempts and provide early warning of potential exploitation attempts. The fix addresses the root cause by ensuring that all registration requests are validated against the current system configuration, thereby preventing unauthorized account creation even when the application is in a state where registration should be disabled.