CVE-2025-63639: FAQ Bot With AI Assistant XSS Vulnerability

CVE-2025-63639 Overview

CVE-2025-63639 is a Cross-Site Scripting (XSS) vulnerability in the Sourcecodester FAQ Bot with AI Assistant v1.0. The chat feature fails to sanitize user-supplied input before rendering it in the browser. Attackers can inject HTML or JavaScript payloads into chat messages, and the code executes when any user views the conversation. The flaw is tracked under CWE-79 and requires user interaction to trigger.

Critical Impact
Attackers can execute arbitrary JavaScript in the browser context of victims, enabling session theft, credential harvesting, and unauthorized actions on behalf of the user.

Affected Products

Sourcecodester FAQ Bot with AI Assistant v1.0
remyandrade:faq_bot_with_ai_assistant:1.0
Deployments using the vulnerable chat component

Discovery Timeline

2025-11-07 - CVE-2025-63639 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-63639

Vulnerability Analysis

The chat feature in the FAQ Bot application accepts user input and renders it directly into the Document Object Model (DOM) without HTML entity encoding or output sanitization. When a user submits a chat message containing HTML tags or <script> payloads, the application treats the string as markup rather than plain text. Any subsequent viewer of the conversation triggers execution of the injected code within their browser session.

The scope is marked as changed, meaning code injected into the chat component can affect resources beyond the vulnerable component itself. Confidentiality and integrity impacts are limited, and there is no direct availability impact. Exploitation requires the victim to view the poisoned conversation, satisfying the user interaction requirement.

Root Cause

The root cause is improper neutralization of input during web page generation. The application concatenates user-controlled chat content into HTML output without escaping reserved characters such as <, >, ", and '. No Content Security Policy (CSP) or output encoding layer intercepts the payload before it reaches the browser parser.

Attack Vector

An unauthenticated attacker sends a crafted chat message containing malicious HTML or JavaScript. The payload is stored or reflected within the conversation view. When another user opens the chat, the browser parses the payload as executable script. Consult the GitHub CVE-2025-63639 Research writeup for reproduction details.

Detection Methods for CVE-2025-63639

Indicators of Compromise

Chat messages containing <script>, onerror=, onload=, or javascript: substrings in application logs or database records.
Outbound HTTP requests from user browsers to unfamiliar domains shortly after loading a chat conversation.
Unexpected cookie access or document.cookie references appearing in browser telemetry.

Detection Strategies

Inspect stored chat records for HTML tags, event handler attributes, and encoded script payloads.
Deploy a Web Application Firewall (WAF) rule set targeting reflected and stored XSS signatures on the chat endpoint.
Enable browser-side CSP violation reporting to surface injection attempts against the FAQ Bot interface.

Monitoring Recommendations

Monitor authentication logs for session anomalies following chat interactions, such as impossible-travel logins reusing stolen cookies.
Alert on new outbound domains referenced by client-side scripts served from the FAQ Bot origin.
Correlate chat submission events with unusual DOM modification patterns captured by endpoint browser telemetry.

How to Mitigate CVE-2025-63639

Immediate Actions Required

Restrict access to the FAQ Bot application until a sanitization fix is applied.
Purge existing chat history of stored payloads containing HTML tags or JavaScript.
Notify users to avoid opening untrusted conversations in the vulnerable interface.

Patch Information

No vendor patch is documented in the NVD entry for CVE-2025-63639 at the time of publication. Operators should track the GitHub CVE-2025-63639 Research and the SourceCodester FAQ Bot Source Code project page for updates. In the interim, apply source-level fixes to encode user input before rendering.

Workarounds

Implement HTML entity encoding on all chat message rendering paths, escaping <, >, &, ", and '.
Deploy a strict Content Security Policy (CSP) that disallows inline scripts and restricts script sources.
Introduce a server-side allowlist filter that rejects chat submissions containing HTML tags or event handler attributes.
Set the HttpOnly and Secure flags on session cookies to reduce impact of successful script execution.

bash

# Example nginx Content-Security-Policy header to blunt XSS execution
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;