CVE-2021-42169
📋 TL;DR
This CVE describes a critical SQL injection vulnerability in the Simple Payroll System with Dynamic Tax Bracket PHP application that allows attackers to bypass authentication and gain admin access. The vulnerability affects all deployments of this specific open-source payroll software where the login form is exposed. Attackers can exploit this without authentication to compromise the entire system.
💻 Affected Systems
- Simple Payroll System with Dynamic Tax Bracket in PHP using SQLite
📦 What is this software?
Simple Payroll System With Dynamic Tax Bracket by Simple Payroll System With Dynamic Tax Bracket Project
View all CVEs affecting Simple Payroll System With Dynamic Tax Bracket →
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with admin access leading to data theft, payroll manipulation, financial fraud, and potential lateral movement to other systems.
Likely Case
Unauthorized admin access allowing payroll data theft, modification of employee records, and potential ransomware deployment.
If Mitigated
Failed login attempts logged, but no successful exploitation due to proper input validation and parameterized queries.
🎯 Exploit Status
Public exploit code is available on Exploit-DB and GitHub. The attack requires minimal technical skill as it's a straightforward SQL injection in the login form.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
No official patch available. Recommended to implement parameterized queries in the login.php file or replace the entire application with a secure alternative.
🔧 Temporary Workarounds
Implement Input Validation and Parameterized Queries
allModify the login.php file to use prepared statements with parameterized queries instead of direct string concatenation.
Edit login.php and replace SQL queries with: $stmt = $conn->prepare('SELECT * FROM users WHERE username = ? AND password = ?'); $stmt->execute([$username, $password]);
Web Application Firewall (WAF) Rules
allDeploy WAF rules to block SQL injection patterns in login requests.
Configure WAF to block requests containing SQL keywords like UNION, SELECT, OR 1=1, --, #, ' OR '1'='1 in username parameter
🧯 If You Can't Patch
- Immediately take the payroll system offline and migrate to a secure alternative
- Implement network segmentation to isolate the vulnerable system and restrict access to authorized IPs only
🔍 How to Verify
Check if Vulnerable:
Test the login form with SQL injection payloads like: admin' OR '1'='1 or admin'-- in the username field. If login succeeds without correct credentials, system is vulnerable.Check Version:
Check the source code files for modification dates and compare with known vulnerable versions. No versioning system is built into this application.Verify Fix Applied:
Attempt the same SQL injection payloads after implementing fixes. Login should fail with incorrect credentials regardless of SQL payload.📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts with SQL syntax in username field
- Successful admin login from unusual IP addresses
- Login attempts containing SQL keywords like UNION, SELECT, OR, --
Network Indicators:
- HTTP POST requests to login.php with SQL injection payloads in parameters
- Unusual database query patterns from web server
SIEM Query:
source="web_logs" AND (uri_path="/login.php" OR uri_path="/admin/login.php") AND (request_body LIKE "%OR%1%1%" OR request_body LIKE "%UNION%SELECT%" OR request_body LIKE "%--%" OR request_body LIKE "%#%")