CVE-2026-16202 Overview
CVE-2026-16202 is a reflected cross-site scripting (XSS) vulnerability in SourceCodester Class and Exam Timetabling System 1.0. The flaw resides in the /CYS.php endpoint, where the course parameter is not properly sanitized before being reflected in the response. Remote attackers can inject arbitrary JavaScript that executes in a victim's browser session when the crafted request is processed. The exploit has been publicly disclosed, increasing the likelihood of opportunistic abuse against exposed instances. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation).
Critical Impact
Attackers can execute arbitrary JavaScript in an authenticated user's browser to hijack sessions, steal credentials, or perform actions on behalf of the victim.
Affected Products
- SourceCodester Class and Exam Timetabling System 1.0
- Vulnerable file: /CYS.php
- Vulnerable parameter: course
Discovery Timeline
- 2026-07-19 - CVE-2026-16202 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-16202
Vulnerability Analysis
The vulnerability affects the /CYS.php script in the SourceCodester Class and Exam Timetabling System 1.0. The application accepts the course HTTP parameter and reflects its value into the rendered HTML output without applying context-appropriate encoding or input validation. An attacker crafts a URL containing JavaScript payloads in the course argument and delivers it to a target user. When the victim opens the link while authenticated to the application, the injected script executes with the privileges of that session.
The attack is network-reachable and requires low-privileged access along with user interaction, per the CVSS 4.0 vector. Public disclosure of the exploit steps in the referenced VulDB and GitHub advisories lowers the barrier for reproduction by unsophisticated attackers.
Root Cause
The root cause is missing output encoding on user-controlled input. The course parameter received by /CYS.php is embedded directly into the HTML response without HTML entity encoding or allowlist validation. This is a classic reflected XSS pattern falling under CWE-79.
Attack Vector
An attacker constructs a malicious link targeting /CYS.php with a JavaScript payload in the course query string parameter. Social engineering via email, chat, or a compromised web page delivers the link to an authenticated user. When the victim clicks the link, the browser executes the payload in the origin context of the vulnerable application, enabling session token theft, keystroke capture, credential harvesting through injected forms, or unauthorized state-changing requests.
No verified proof-of-concept code is republished here. Technical exploitation details are documented in the GitHub Issue Discussion and the VulDB CVE Details.
Detection Methods for CVE-2026-16202
Indicators of Compromise
- HTTP requests to /CYS.php containing script-related keywords such as <script>, onerror=, javascript:, or URL-encoded equivalents in the course parameter.
- Web server access logs showing anomalous course parameter values that include angle brackets, event handlers, or long encoded payloads.
- Outbound browser traffic from user workstations to attacker-controlled domains immediately after visiting the application.
Detection Strategies
- Deploy web application firewall (WAF) signatures that inspect query strings for reflected XSS patterns targeting the course argument.
- Enable server-side request logging with full URI capture and alert on payloads matching common XSS fuzzing patterns.
- Correlate endpoint browser telemetry with web server logs to detect script execution originating from /CYS.php responses.
Monitoring Recommendations
- Monitor for unusual referrer chains ending at /CYS.php requests, which can indicate phishing-delivered exploit links.
- Track authentication events for account takeover indicators such as session token reuse from new IPs after a suspicious link click.
- Review Content Security Policy (CSP) violation reports for blocked inline script execution on application pages.
How to Mitigate CVE-2026-16202
Immediate Actions Required
- Restrict external access to the Class and Exam Timetabling System until output encoding is implemented on the course parameter.
- Apply a WAF rule that blocks or sanitizes requests to /CYS.php containing HTML metacharacters in the course argument.
- Notify users of the application to avoid clicking untrusted links referencing the timetabling system.
Patch Information
No vendor patch has been published at the time of NVD listing. SourceCodester project maintainers have not released a fixed version. Monitor the SourceCodester Security Blog and the VulDB Vulnerability Overview for remediation updates.
Workarounds
- Implement server-side HTML entity encoding on the course parameter before rendering it in the response, using a vetted encoding library.
- Apply an allowlist input filter that accepts only expected characters for course identifiers, rejecting angle brackets, quotes, and control characters.
- Enforce a strict Content Security Policy that disallows inline script execution and restricts script sources to trusted origins.
- Set the HttpOnly and Secure flags on session cookies to reduce the impact of successful script execution.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
