CVE-2016-9849 in phpMyAdmin
Summary
by MITRE
An issue was discovered in phpMyAdmin. It is possible to bypass AllowRoot restriction ($cfg['Servers'][$i]['AllowRoot']) and deny rules for username by using Null Byte in the username. All 4.6.x versions (prior to 4.6.5), 4.4.x versions (prior to 4.4.15.9), and 4.0.x versions (prior to 4.0.10.18) are affected.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9849 represents a critical authentication bypass flaw in phpMyAdmin that undermines fundamental security controls designed to restrict root access and enforce username-based access policies. This weakness specifically targets the AllowRoot configuration parameter which is intended to prevent unauthorized root login attempts by setting $cfg['Servers'][$i]['AllowRoot'] to false. The flaw exploits a null byte injection technique that allows attackers to circumvent these security restrictions through manipulation of the username parameter during authentication attempts.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within phpMyAdmin's authentication handling mechanism. When a username containing a null byte character is submitted to the authentication process, the application fails to properly process or sanitize this input before performing access control checks. This null byte injection allows the authentication system to interpret the username differently than intended, effectively bypassing the AllowRoot restriction and potentially circumventing username-based deny rules that should prevent specific users from accessing the database management interface. The vulnerability affects multiple version streams of phpMyAdmin including 4.6.x prior to 4.6.5, 4.4.x prior to 4.4.15.9, and 4.0.x prior to 4.0.10.18, indicating a widespread impact across the software's release history.
The operational impact of this vulnerability is severe as it enables unauthorized access to database management interfaces that should be restricted to privileged users only. Attackers can leverage this flaw to gain administrative access to database servers through phpMyAdmin without proper authorization, potentially leading to data breaches, privilege escalation, and unauthorized database modifications. The vulnerability particularly affects environments where phpMyAdmin is deployed with AllowRoot set to true but where additional access controls are implemented to restrict specific user accounts. This creates a dangerous scenario where even if individual user accounts are denied access, the null byte injection technique can bypass these restrictions and provide unauthorized administrative access to database systems.
This vulnerability aligns with CWE-170, which addresses improper handling of null bytes in input validation, and represents a classic example of a null byte injection attack that has been documented in various security frameworks including those referenced in the ATT&CK framework under credential access and privilege escalation techniques. The flaw demonstrates how insufficient input sanitization can create persistent security weaknesses that affect authentication mechanisms and access controls. Organizations using phpMyAdmin should immediately implement the available patches for their specific version ranges to address this vulnerability, as the null byte injection technique can be easily automated and exploited without requiring advanced technical skills. The recommended mitigation strategy involves upgrading to patched versions of phpMyAdmin, specifically versions 4.6.5, 4.4.15.9, and 4.0.10.18 respectively, while also implementing additional monitoring for suspicious authentication attempts that may indicate exploitation of this vulnerability.