CVE-2017-9091 in Disk
Summary
by MITRE
/admin/loginc.php in Allen Disk 1.6 doesn't check if isset($_SESSION['captcha']['code']) == 1, which leads to CAPTCHA bypass by emptying $_POST['captcha'].
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-9091 affects Allen Disk 1.6, a web-based file management system that exposes a critical authentication flaw in its login mechanism. This issue resides within the /admin/loginc.php script where the application fails to properly validate session-based CAPTCHA integrity before proceeding with authentication checks. The flaw represents a significant security weakness that undermines the intended protection mechanisms designed to prevent automated login attempts and brute force attacks.
The technical implementation of this vulnerability stems from inadequate input validation and session management within the authentication flow. Specifically, the application does not verify whether the CAPTCHA session variable $_SESSION['captcha']['code'] exists and contains valid data before accepting login credentials. This oversight allows malicious actors to bypass the CAPTCHA protection mechanism by simply submitting an empty or null value for the captcha field in the POST request. The vulnerability is classified under CWE-284 Access Control Bypass, as it permits unauthorized access through the circumvention of authentication controls that should have been enforced.
The operational impact of this vulnerability is substantial as it effectively neutralizes the CAPTCHA protection that serves as a crucial defense against automated login attacks. Attackers can exploit this weakness to perform repeated login attempts without CAPTCHA verification, significantly increasing their chances of successful authentication through brute force methods. This vulnerability particularly affects systems where the CAPTCHA mechanism was intended to provide protection against bots and automated attack vectors, making it a prime target for credential stuffing and dictionary attack campaigns. The bypass capability directly undermines the principle of least privilege and weakens the overall authentication security posture of the application.
Security professionals should implement immediate mitigations to address this vulnerability by ensuring proper session validation and input sanitization in the authentication process. The recommended fix involves adding explicit checks to verify that the CAPTCHA session variable exists and contains valid data before proceeding with authentication validation. This remediation aligns with ATT&CK technique T1110.003 Credential Stuffing and addresses the broader category of authentication bypass vulnerabilities. Organizations should also consider implementing additional security controls such as account lockout mechanisms, rate limiting for login attempts, and monitoring for suspicious authentication patterns. The vulnerability demonstrates the critical importance of proper session management and input validation in web applications, emphasizing that even seemingly simple security controls like CAPTCHA can be rendered ineffective through inadequate implementation.