Bypassing Authentication Gates: SQL Injection (Auth Bypass) on Login Portal

Executive Summary

During an authorized security assessment, a critical SQL Injection (SQLi) vulnerability was identified and validated on the primary login portal of the target web application. By exploiting improper input sanitization in the username field, an unauthenticated external actor can manipulate backend database queries to completely bypass password verification. This allows immediate, unauthorized administrative access to the system without possessing valid credentials.

Vulnerability Type: SQL Injection (CWE-89) / Authentication Bypass
Severity: Critical (CVSS v3.1 Score: 9.8/10)
Target Interface: /app/login.php via the username parameter

Assessment Context

Target Type: Private Enterprise Portal (Internal Audit)
Engagement Type: Authorized Internal Penetration Testing (Grey-box)
Disclosure Status: Responsibly Disclosed & Fully Remediated by the Internal Dev Team.
Bounty/Reward: Internal Pentesting Engagement (Corporate Payroll).

Technical Analysis & Query Breakdown

1. The Flawed Database Query Structure

During initial testing, entering a standard single-quote payload (admin' or 1=1 --) returned a verbose MariaDB database syntax error. The error message explicitly disclosed the underlying dynamic SQL query:

SELECT * FROM users WHERE username = 'admin' or 1=1 --' AND password = '[Base64_Password]' LIMIT 1

SELECT * FROM users WHERE username = 'admin' or 1=1 --' AND password = '[Base64_Password]' LIMIT 1

The Syntax Error Analysis: The database returned error No(1064) because the trailing single quote ' after the comment characters (--) was left dangling, breaking the MariaDB syntax.

2. Crafting the Bypass Payload

To fix the syntax collision, the comment block was balanced by introducing a trailing space and a closing quote: admin' or 1=1 -- '

When the database processes this corrected payload, the resulting query logic becomes:

SELECT * FROM users WHERE username = 'admin' or 1=1 -- ' AND password = '...' LIMIT 1

SELECT * FROM users WHERE username = 'admin' or 1=1 -- ' AND password = '...' LIMIT 1

The Logical Result:

The backend interprets the double-dash (--) as the start of a SQL comment.
This completely ignores and truncates the remaining password verification constraint (AND password = '...').
Since 1=1 is always True, the database returns the first valid administrative record matching the query, granting full session access instantly.

Proof of Concept (PoC) Steps

Navigate to the login endpoint at [https://target-app.com/app/login.php](https://target-app.com/app/login.php).
Input the following payload into the Username field:
admin' or 1=1 -- '
Input any arbitrary value into the Password field.
Click Login.
Observe that the server successfully authenticates the request and redirects to the administrative session dashboard ("Welcome admin").

Risk & Business Impact

Complete Administrative Takeover: Attackers gain immediate dashboard control with high-level privileges.
Data Compromise: Access to restricted business workflows, system configs, customer lists, and financial logs.
Lateral Movement: Administrative web portal compromise is often used as a stepping stone to execute further internal attacks.

Remediation & Mitigation Strategy

Perimeter firewalls cannot permanently protect against bad database query construction. The application code must be hardened directly:

1. Enforce Prepared Statements (Parameterized Queries)

Never concatenate user inputs directly into SQL command strings. Use PDO (PHP Data Objects) with prepared statements to ensure the database treats input strictly as data, not executable code:

// Secure PHP implementation using PDO
$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username LIMIT 1');
$stmt->execute(['username' => $username]);
$user = $stmt->fetch();
if ($user && password_verify($password, $user['password'])) {
    // Securely login
}

// Secure PHP implementation using PDO
$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username LIMIT 1');
$stmt->execute(['username' => $username]);
$user = $stmt->fetch();
if ($user && password_verify($password, $user['password'])) {
    // Securely login
}

2. Disable Verbose Database Errors in Production

Configure the web server to suppress raw SQL exception outputs to the client. This prevents attackers from easily profiling the database schema or query structures during initial testing phases.

Disclaimer & Contact

This security assessment was conducted legally with prior authorization and written permission from the target organization. All sensitive details and company identifiers have been strictly obfuscated for confidentiality compliance.

LinkedIn: https://www.linkedin.com/in/mustafa-mohamed-0a77a1197/
Github: https://github.com/MustafaSEC404

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