CVE-2026-29861: PHP-MYSQL User Login System SQLi Flaw

CVE-2026-29861 Overview

CVE-2026-29861 is a critical SQL injection vulnerability discovered in PHP-MYSQL-User-Login-System v1.0. The vulnerability exists in the login.php file and can be exploited through the username parameter, allowing attackers to manipulate SQL queries executed by the application's backend database.

Critical Impact

This SQL injection vulnerability enables unauthenticated attackers to bypass authentication, extract sensitive data from the database, modify or delete records, and potentially achieve remote code execution depending on database configuration and privileges.

Affected Products

• PHP-MYSQL-User-Login-System v1.0
• Applications derived from or implementing the vulnerable login component

Discovery Timeline

• April 10, 2026 - CVE-2026-29861 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-29861

Vulnerability Analysis

This SQL injection vulnerability (CWE-89: Improper Neutralization of Special Elements used in an SQL Command) occurs when the application fails to properly sanitize user-supplied input in the username parameter before incorporating it into SQL queries. The vulnerability is accessible over the network without requiring authentication or user interaction, making it particularly dangerous for exposed systems.

The attack surface is the login form's username field, which directly concatenates user input into database queries without adequate input validation or parameterized queries. This allows attackers to inject arbitrary SQL commands that are then executed with the privileges of the database user configured for the application.

Root Cause

The root cause of CVE-2026-29861 is improper input validation and the use of string concatenation to build SQL queries in the login.php authentication handler. Rather than using prepared statements or parameterized queries, the application directly embeds the username parameter value into the SQL query string, enabling injection attacks.

Attack Vector

The vulnerability is exploited by submitting specially crafted SQL syntax through the username parameter in the login form. An attacker can submit malicious input that breaks out of the intended query structure and executes arbitrary SQL commands. Common attack techniques include:

• Authentication bypass using techniques like ' OR '1'='1 to manipulate WHERE clauses
• UNION-based attacks to extract data from other database tables
• Time-based blind SQL injection to infer database contents
• Stacked queries (if supported by the database driver) to execute additional statements including INSERT, UPDATE, or DELETE operations

For detailed technical analysis, refer to the GitHub PoC Repository.

Detection Methods for CVE-2026-29861

Indicators of Compromise

• Unusual or malformed values in web server access logs for login.php requests containing SQL syntax characters (', ", --, /*, */, OR, UNION)
• Database error messages appearing in application responses or logs
• Unexpected database queries or anomalous query patterns in database audit logs
• Failed authentication attempts with usernames containing special characters or SQL keywords

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block SQL injection patterns in the username parameter
• Deploy database activity monitoring to identify anomalous SQL queries originating from the web application
• Configure intrusion detection systems (IDS) with signatures for common SQL injection attack patterns
• Enable verbose logging on the login.php endpoint and correlate with database query logs

Monitoring Recommendations

• Monitor HTTP POST requests to login.php for payloads containing SQL metacharacters and injection keywords
• Set up alerts for database errors or exceptions triggered by the web application's database user
• Track authentication success rates and investigate sudden changes in login patterns
• Review database query logs for unusual SELECT, UNION, or data exfiltration patterns

How to Mitigate CVE-2026-29861

Immediate Actions Required

• Implement input validation and sanitization for all user-supplied parameters, particularly the username field in login.php
• Replace dynamic SQL query construction with parameterized queries or prepared statements
• Apply the principle of least privilege to database accounts used by the application
• Deploy a Web Application Firewall (WAF) as a temporary protective measure while implementing code fixes

Patch Information

No official vendor patch has been published at this time. Users should implement the code-level mitigations described below or consider replacing this authentication system with a secure alternative. Monitor the GitHub PoC Repository for updates and additional remediation guidance.

Workarounds

• Migrate all SQL queries to use PDO or MySQLi with prepared statements and parameterized queries
• Implement strict input validation allowing only expected characters in the username field (alphanumeric, limited special characters)
• Consider temporarily disabling or restricting access to the affected login functionality until a permanent fix is deployed
• Use a web application firewall to filter malicious requests targeting the vulnerable endpoint

# Example PHP configuration hardening for MySQL connections
# In php.ini or application configuration
# Disable multiple statements to reduce stacked query attack surface
mysqli.allow_local_infile = Off
mysqli.allow_persistent = Off