CVE-2017-9090 in Disk
Summary
by MITRE
reg.php in Allen Disk 1.6 doesn't check if isset($_SESSION['captcha']['code'])==1, which makes it possible to bypass the CAPTCHA via an empty $_POST['captcha'].
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-9090 resides within the reg.php script of Allen Disk version 1.6, representing a critical security flaw that undermines the application's user registration process. This issue stems from insufficient input validation and session management practices that allow malicious actors to circumvent essential security measures designed to prevent automated account creation. The vulnerability specifically targets the CAPTCHA validation mechanism, which serves as a fundamental barrier against bot-driven registration attempts that could lead to spam accounts or abuse of the system resources.
The technical implementation flaw occurs when the application fails to properly verify the existence of a CAPTCHA code within the user session before processing registration requests. The vulnerability manifests when the system does not check if isset($_SESSION['captcha']['code']) equals 1, creating a logical gap that enables attackers to bypass the CAPTCHA validation entirely. This oversight allows an attacker to submit a registration form with an empty $_POST['captcha'] parameter, effectively rendering the CAPTCHA protection useless and permitting unauthorized account creation without proper verification. The flaw demonstrates a classic example of improper session validation and input sanitization, where the application assumes the presence of expected session data without proper verification.
The operational impact of this vulnerability extends beyond simple account registration abuse, potentially enabling a range of malicious activities including spam account creation, denial of service attacks through automated registration, and exploitation of other application features that depend on legitimate user accounts. Attackers can leverage this weakness to flood the system with fake accounts, consume server resources unnecessarily, and potentially use these accounts for further attacks such as forum spam, comment spam, or other forms of content abuse. The vulnerability also represents a failure in the principle of least privilege and proper access control implementation, as it allows unauthenticated or improperly authenticated users to bypass security controls that should be mandatory for account creation.
This vulnerability aligns with CWE-20, which describes "Improper Input Validation," and CWE-346, "Origin Validation Error," as it demonstrates poor validation of user inputs and session data integrity. From an ATT&CK perspective, this weakness maps to T1078, "Valid Accounts," as it enables adversaries to create legitimate-looking accounts without proper verification, and potentially to T1499, "Endpoint Denial of Service," through resource exhaustion via automated account creation. The flaw also relates to T1190, "Exploit Public-Facing Application," as it represents an exploitable weakness in a publicly accessible registration interface. Organizations should implement proper session validation checks, ensure that all session data is properly verified before processing, and establish robust input validation mechanisms to prevent similar vulnerabilities from occurring.
The recommended mitigations include implementing comprehensive session validation checks that verify the existence and validity of CAPTCHA codes before processing registration requests, ensuring that all session variables are properly initialized and validated, and adding proper input sanitization to prevent empty or malformed CAPTCHA submissions. Developers should also implement rate limiting mechanisms to prevent excessive registration attempts and consider implementing more robust CAPTCHA solutions that cannot be easily bypassed through simple parameter manipulation. Additionally, regular security code reviews and automated vulnerability scanning should be implemented to identify similar issues in other parts of the application and prevent regression of such flaws in future releases.