CVE-2017-18264 in phpMyAdmin
Summary
by MITRE
An issue was discovered in libraries/common.inc.php in phpMyAdmin 4.0 before 4.0.10.20, 4.4.x, 4.6.x, and 4.7.0 prereleases. The restrictions caused by $cfg['Servers'][$i]['AllowNoPassword'] = false are bypassed under certain PHP versions (e.g., version 5). This can allow the login of users who have no password set even if the administrator has set $cfg['Servers'][$i]['AllowNoPassword'] to false (which is also the default). This occurs because some implementations of the PHP substr function return false when given '' as the first argument.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2017-18264 represents a critical authentication bypass flaw in phpMyAdmin versions prior to 4.0.10.20, 4.4.x, and 4.6.x releases. This issue stems from a fundamental flaw in the phpMyAdmin library implementation where the security configuration parameter $cfg['Servers'][$i]['AllowNoPassword'] = false is effectively ignored under specific PHP runtime conditions. The vulnerability manifests when the PHP substr function behaves differently than expected when processing empty string inputs, creating a security gap that allows unauthorized access to database systems.
The technical root cause of this vulnerability lies in the improper handling of PHP's substr function behavior when it receives an empty string as its first argument. In certain PHP versions, particularly PHP 5.x, the substr function returns false instead of an empty string when processing empty inputs. This unexpected behavior in the phpMyAdmin codebase causes the authentication logic to incorrectly evaluate whether a user has provided a password, leading to the bypass of the intended security restriction. The flaw operates at the application logic level and specifically affects the validation mechanism that should prevent passwordless logins when explicitly disabled by administrators.
This vulnerability creates significant operational impact by undermining the fundamental authentication security model of phpMyAdmin installations. Administrators who configure $cfg['Servers'][$i]['AllowNoPassword'] = false expecting to prevent passwordless access are deceived by this bypass, potentially allowing malicious actors to gain unauthorized database access. The security implications extend beyond simple unauthorized access as this vulnerability can enable data exfiltration, modification of database contents, and potential privilege escalation within the database environment. The vulnerability affects a wide range of phpMyAdmin versions and is particularly concerning because it operates silently, allowing unauthorized access without generating explicit authentication errors.
The security implications of this vulnerability align with CWE-284, which addresses improper access control mechanisms, and can be categorized under ATT&CK technique T1110.003 for credential access through password guessing and T1078 for valid accounts usage. Organizations using affected phpMyAdmin versions face the risk of unauthorized database access, which could result in data breaches, compliance violations, and system compromise. The vulnerability is particularly dangerous in environments where phpMyAdmin is exposed to untrusted networks or where database administrators have configured strict authentication policies. The bypass mechanism operates at the application layer and can be exploited remotely without requiring special privileges or advanced technical skills.
The recommended mitigation strategy involves immediate upgrading to phpMyAdmin versions 4.0.10.20, 4.4.x, or 4.6.x releases that contain the patched implementation. System administrators should also review and validate their phpMyAdmin configuration files to ensure that $cfg['Servers'][$i]['AllowNoPassword'] is properly set to false and verify that all database access controls are functioning as intended. Additional security measures include implementing network-level restrictions, using strong authentication mechanisms, and monitoring for unauthorized access attempts. Organizations should also conduct comprehensive vulnerability assessments to identify other potentially affected systems and ensure that all phpMyAdmin installations are updated to supported versions that address this specific authentication bypass vulnerability.