CVE-2016-9182 in Exponent
Summary
by MITRE
Exponent CMS 2.4 uses PHP reflection to call a method of a controller class, and then uses the method name to check user permission. But, the method name in PHP reflection is case insensitive, and Exponent CMS permits undefined actions to execute by default, so an attacker can use a capitalized method name to bypass the permission check, e.g., controller=expHTMLEditor&action=preview&editor=ckeditor and controller=expHTMLEditor&action=Preview&editor=ckeditor. An anonymous user will be rejected for the former but can access the latter.
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Analysis
by VulDB Data Team • 09/29/2022
The vulnerability in Exponent CMS 2.4 represents a critical authorization bypass flaw that stems from improper handling of method names during PHP reflection operations. This issue falls under the category of insecure authorization mechanisms and can be classified as CWE-285, which deals with insufficient authorization checks. The CMS utilizes PHP's reflection capabilities to dynamically invoke controller methods based on user input, specifically the action parameter that determines which method to execute. The system's design flaw lies in its case-insensitive method name comparison during reflection, combined with a permissive default policy that allows undefined actions to execute without proper permission verification.
The technical implementation of this vulnerability exploits the inherent case-insensitive nature of PHP reflection method resolution while leveraging the CMS's default configuration that permits undefined actions. When an attacker submits a request with a capitalized method name such as Preview instead of preview, the PHP reflection mechanism correctly identifies the method regardless of case sensitivity, but the permission checking logic fails to account for this discrepancy. This creates a scenario where the system accepts the capitalized method name as valid and proceeds with execution, while the original lowercase version would have been rejected due to insufficient permissions. The vulnerability specifically affects the expHTMLEditor controller where the preview action can be accessed through different case variations, allowing anonymous users to bypass authentication mechanisms that should restrict access to privileged functionality.
The operational impact of this vulnerability is significant as it enables unauthorized access to administrative features that should only be available to authenticated users with proper privileges. Attackers can exploit this weakness to gain access to sensitive functionality within the CMS, potentially leading to complete system compromise. The vulnerability exists in the controller method dispatching logic and permission validation process, creating a pathway for privilege escalation attacks. From an attack chain perspective, this vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and T1484 which covers abuse of privileges, as it allows attackers to bypass normal authorization controls through method name manipulation. The default permissive configuration of allowing undefined actions to execute creates an attack surface that directly enables this bypass mechanism.
Mitigation strategies for this vulnerability should focus on implementing strict case-sensitive method name validation and ensuring that all controller actions are explicitly defined and validated before execution. Organizations should disable the default permissive behavior that allows undefined actions and instead implement a whitelist approach where only explicitly permitted methods can be executed. The CMS should enforce stricter authorization checks that account for case sensitivity during method name comparison and validate all incoming action parameters against a predefined list of valid methods. Additionally, implementing proper input sanitization and parameter validation mechanisms will help prevent attackers from manipulating method names to bypass authorization checks. Security patches should be applied to update the CMS to versions that address this specific authorization bypass vulnerability, and administrators should conduct thorough security reviews of all controller method dispatching logic to identify similar patterns that might exist in other parts of the application.