CVE-2026-4973 Overview
A Cross-Site Scripting (XSS) vulnerability has been identified in SourceCodester Online Quiz System up to version 1.0. The vulnerability exists in the endpoint/add-question.php file, where improper input validation of the quiz_question argument allows attackers to inject malicious scripts. This stored XSS vulnerability can be exploited remotely by authenticated users to execute arbitrary JavaScript code in the context of other users' browsers.
Critical Impact
Authenticated attackers can inject malicious scripts through the quiz question functionality, potentially leading to session hijacking, credential theft, or unauthorized actions on behalf of other users including administrators.
Affected Products
- SourceCodester Online Quiz System 1.0
- SourceCodester Online Quiz System versions prior to 1.0
Discovery Timeline
- 2026-03-27 - CVE-2026-4973 published to NVD
- 2026-03-30 - Last updated in NVD database
Technical Details for CVE-2026-4973
Vulnerability Analysis
This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting (XSS). The flaw exists in the quiz question creation functionality where user-supplied input is not properly sanitized before being stored and rendered back to users.
When a user with quiz creation privileges submits a question through the endpoint/add-question.php endpoint, the quiz_question parameter accepts arbitrary input including HTML and JavaScript code. This malicious content is then stored in the database and executed when other users view the quiz questions, making this a stored (persistent) XSS vulnerability.
The attack requires low privileges (authenticated user with quiz creation access) and passive user interaction (victim must view the affected quiz content). While the vulnerability does not directly impact confidentiality or availability, it allows modification of displayed content and can be leveraged for more sophisticated attacks.
Root Cause
The root cause is the absence of proper input sanitization and output encoding for the quiz_question parameter in the add-question.php endpoint. The application fails to implement adequate security controls to prevent HTML and script injection, allowing raw user input to be stored and subsequently rendered without escaping.
Attack Vector
The attack is network-based and requires an authenticated attacker with privileges to create quiz questions. The attacker crafts a malicious quiz question containing JavaScript code and submits it through the vulnerable endpoint. When administrators or other users view the quiz questions, the injected script executes in their browser context.
The exploitation flow involves:
- Authenticating to the Online Quiz System with quiz creation privileges
- Navigating to the add question functionality
- Injecting malicious JavaScript code in the quiz_question field
- Waiting for victims to view the affected quiz content
- Harvesting stolen credentials, session tokens, or executing unauthorized actions
A proof-of-concept demonstrating this vulnerability is publicly available through the GitHub Gist PoC Repository.
Detection Methods for CVE-2026-4973
Indicators of Compromise
- Unexpected JavaScript or HTML tags in quiz question database entries
- Anomalous HTTP requests to endpoint/add-question.php containing script tags or encoded payloads
- User reports of unexpected browser behavior when viewing quiz content
- Session anomalies or unauthorized actions following quiz page views
Detection Strategies
- Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in POST requests to add-question.php
- Enable application logging for all quiz question submissions and review for suspicious patterns
- Deploy Content Security Policy (CSP) headers and monitor for violations
- Conduct regular database audits for stored XSS payloads in quiz-related tables
Monitoring Recommendations
- Monitor application logs for POST requests to endpoint/add-question.php containing suspicious characters or encoded payloads
- Set up alerts for CSP violation reports indicating potential XSS attempts
- Review user activity logs for unusual quiz creation patterns or bulk submissions
- Implement real-time monitoring for JavaScript execution anomalies on quiz pages
How to Mitigate CVE-2026-4973
Immediate Actions Required
- Restrict access to quiz creation functionality to trusted administrators only
- Implement input validation to reject quiz questions containing HTML or script tags
- Deploy output encoding on all dynamic content rendered from user input
- Review existing quiz questions in the database for malicious content and sanitize if necessary
Patch Information
No official patch has been released by SourceCodester at this time. Organizations using the Online Quiz System should implement the workarounds below and monitor the SourceCodester website for security updates. Additional vulnerability details are available through VulDB #353860.
Workarounds
- Implement server-side input validation to strip or encode HTML entities from the quiz_question parameter
- Apply output encoding (htmlspecialchars or equivalent) when displaying quiz questions
- Deploy Content Security Policy (CSP) headers to prevent inline script execution
- Consider using a web application firewall to filter XSS payloads at the network layer
# Example Apache .htaccess CSP header configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"
# Example nginx CSP header configuration
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'";
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
