CVE-2025-63709: Simple To-Do List System XSS Vulnerability

CVE-2025-63709 Overview

CVE-2025-63709 is a stored Cross-Site Scripting (XSS) vulnerability in SourceCodester Simple To-Do List System 1.0, developed by chuck24. The flaw resides in the "Add Tasks" text input, where authenticated users can submit HTML or JavaScript that the application fails to sanitize or encode on output. The injected payload is persisted in the application and executed in the browser of any user who later views the task list.

Critical Impact
Authenticated attackers can execute arbitrary JavaScript in the browser context of other application users, enabling session theft, credential harvesting, and unauthorized actions on behalf of victims.

Affected Products

chuck24 Simple To-Do List System 1.0
SourceCodester PHP Simple To-Do List distribution
CPE: cpe:2.3:a:chuck24:simple_to-do_list_system:1.0

Discovery Timeline

2025-11-10 - CVE-2025-63709 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-63709

Vulnerability Analysis

The vulnerability is classified as Improper Neutralization of Input During Web Page Generation [CWE-79]. The Simple To-Do List System accepts task content from authenticated users through the "Add Tasks" text input and stores it in the backend datastore. When the application later renders the task list, it emits the stored value directly into the HTML response without applying output encoding or contextual escaping.

Because the payload is persistent, exploitation does not require the attacker to trick a victim into visiting a malicious URL. Any user account with task-creation privileges can plant the payload, and it will execute for every subsequent viewer of the affected task. This qualifies as a stored (Type II) XSS condition, which is generally more impactful than reflected XSS because it does not depend on social engineering the victim per session.

Root Cause

The root cause is missing input sanitization and missing output encoding in the task rendering path. The application trusts the string supplied to the task field and inserts it into the DOM as raw HTML. There is no allow-listing of permitted tags, no HTML entity encoding of <, >, ", and ', and no Content Security Policy (CSP) enforcement to restrict inline script execution.

Attack Vector

An authenticated attacker submits a task containing a script payload through the "Add Tasks" form. The malicious task is persisted to the underlying database. When a legitimate user, including a higher-privileged administrator, opens the task view, the browser parses the injected markup and executes the attacker-controlled JavaScript. The scope change indicates the payload can act outside the vulnerable component's security context, for example by accessing session cookies, invoking authenticated API endpoints, defacing the UI, or redirecting the user to a phishing page. Additional research and proof-of-concept material is documented in the CVE-2025-63709 research repository.

No verified exploit code is published in the enriched CVE data. See the linked research repository and the SourceCodester PHP Todo List product page for further technical context.

Detection Methods for CVE-2025-63709

Indicators of Compromise

Task records in the application database containing HTML tags such as <script>, <img onerror=>, <svg onload=>, or javascript: URIs.
Outbound HTTP requests from user browsers to unfamiliar domains immediately after loading the task list view.
Unexpected session cookie transmissions or API calls originating from users who were viewing the To-Do List application.

Detection Strategies

Review web server access logs for POST requests to the task creation endpoint containing URL-encoded angle brackets, event handler attributes, or script keywords.
Deploy a Web Application Firewall (WAF) rule set that inspects task field submissions for XSS signatures and blocks or alerts on matches.
Perform periodic database queries against the task storage table looking for stored HTML or JavaScript tokens.

Monitoring Recommendations

Enable browser-side Content Security Policy (CSP) violation reporting to surface script injections that bypass server-side controls.
Monitor authentication logs for session anomalies, such as concurrent sessions or geolocation shifts, following task view activity.
Alert on anomalous DOM-based network requests from application origins using client-side telemetry or a runtime application self-protection (RASP) agent.

How to Mitigate CVE-2025-63709

Immediate Actions Required

Restrict access to the Simple To-Do List System to trusted users until a patched version is available.
Audit the task database and remove any stored records containing HTML or scripting payloads.
Rotate session tokens and credentials for any user who may have viewed a malicious task.

Patch Information

No official vendor patch is referenced in the NVD entry at the time of publication. Consult the CVE-2025-63709 research repository and the SourceCodester project page for updates. Operators should apply contextual output encoding in the task rendering templates and validate input on the server side before persistence.

Workarounds

Apply HTML entity encoding to all task fields at render time using PHP functions such as htmlspecialchars($value, ENT_QUOTES, 'UTF-8').
Deploy a strict Content Security Policy header that disallows inline scripts, for example Content-Security-Policy: default-src 'self'; script-src 'self'.
Front the application with a WAF configured to block common XSS payloads on the task creation endpoint.
Disable or remove the application from production environments where untrusted users can create tasks.

bash

# Example Nginx configuration adding a restrictive CSP header
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'none'" always;
add_header X-Content-Type-Options "nosniff" always;
add_header X-Frame-Options "DENY" always;