# Cross-Site Scripting (XSS) Analysis Report

## 1. Executive Summary

- **Analysis Status:** Complete  
- **Key Outcome:** One critical reflected XSS vulnerability was identified at the root endpoint (`GET /`) via the `username` query parameter. This vulnerability has been confirmed through live browser testing and 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 confirmed XSS vulnerability.

## 2. Dominant Vulnerability Patterns

**Pattern 1: Server-Side Template Injection Leading to Reflected XSS**  
- **Description:** The application creates a raw Jinja2 `Environment()` instance with `autoescape=False` and directly embeds user input from the `username` query parameter into a template string using string concatenation (`"Welcome " + username + "!"`). This bypasses the framework's safe templating system (which has autoescape enabled) and creates both an SSTI and XSS vulnerability.
- **Root Cause:** Developer created a custom Jinja2 Environment instead of using the existing `templates` object (line 10) which has autoescape enabled by default. The use of `from_string()` with concatenated user input allows arbitrary template syntax and HTML to be injected.
- **Implication:** Any attacker can inject arbitrary HTML and JavaScript into the application response. This is the primary and only XSS vector in the application. No other user input is reflected in HTML contexts.
- **Representative Finding:** XSS-VULN-01

**Pattern 2: Inconsistent Security Architecture**
- **Description:** The same application file (`main.py`) contains TWO different template rendering approaches with vastly different security postures:
  - **Safe path** (line 10, 28-29): Uses `Jinja2Templates` with autoescape enabled for directory listing
  - **Unsafe path** (line 31-33): Creates raw `Environment()` without autoescape for username rendering
- **Implication:** This suggests a lack of security awareness or rushed development. The developer had access to a secure templating system but bypassed it, creating a critical vulnerability.

## 3. Strategic Intelligence for Exploitation

**Content Security Policy (CSP) Analysis**  
- **Current CSP:** NONE - No `Content-Security-Policy` header is present in any HTTP response.
- **Verification:** Tested via curl and browser inspection - confirmed zero CSP protection.
- **Impact:** No restrictions on script execution, inline scripts, or external script sources.
- **Recommendation:** Standard XSS payloads will execute without any CSP bypass required. Use simple payloads like `<script>alert(document.domain)</script>` or `<img src=x onerror=alert('XSS')>`.

**Cookie Security**  
- **Observation:** No session cookies are set by the application. No `Set-Cookie` headers observed.
- **Impact:** Traditional cookie theft via `document.cookie` is not applicable.
- **Authentication Status:** The application has zero authentication mechanisms (confirmed from recon report).
- **Recommendation:** Exploitation should focus on demonstrating XSS execution capability rather than session hijacking. Consider:
  - Proof of arbitrary JavaScript execution
  - Data exfiltration from the page context
  - Phishing attacks via injected fake login forms
  - BeEF hooking for advanced demonstrations

**XSS Protection Headers**
- **X-XSS-Protection:** NOT SET - No browser-based XSS filtering
- **X-Frame-Options:** NOT SET - Page can be framed (clickjacking possible as secondary attack)
- **X-Content-Type-Options:** NOT SET - No MIME sniffing protection
- **Strict-Transport-Security:** NOT SET - No HSTS (application only serves HTTP anyway)

**HTTP Response Headers (Complete Set):**
```
HTTP/1.1 200 OK
date: Wed, 29 Oct 2025 20:28:44 GMT
server: uvicorn
content-length: 13
content-type: text/html; charset=utf-8
```

**Server Information Disclosure:**
- `server: uvicorn` header reveals the application server technology
- Combined with reconnaissance data, full stack is known: FastAPI + Uvicorn + Jinja2

**WAF/Rate Limiting Status:**
- **Web Application Firewall:** NONE detected
- **Rate Limiting:** NONE - Unlimited exploitation attempts confirmed
- **Input Validation:** ZERO - No length limits, no character restrictions
- **Payload Restrictions:** None - All payloads pass through unfiltered

## 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 |
|--------------------------|-------------------------|--------------------------------|----------------|---------|
| `files` variable | `GET /` (directory listing) | Jinja2 autoescape=True (Starlette default) + filesystem-based data source (not user-controllable) | HTML_BODY | SAFE |
| `request` object | Template rendering in index.html | Autoescape enabled, framework-managed object | HTML_BODY | SAFE |

**Detailed Analysis of Secure Path:**

**Directory Listing Template (index.html:23-25):**
- **Data Source:** `list_directory('.')` function (main.py:13-22) which uses `os.walk()` to read filesystem
- **User Control:** NONE - Path is hardcoded to `'.'`, filenames come from actual filesystem
- **Autoescape:** ENABLED - `Jinja2Templates` (line 10) uses Starlette's default `autoescape=True`
- **Template Syntax:** `{{ file }}` - Standard variable interpolation with autoescape
- **Verdict:** SAFE - Even if an attacker could create files with malicious names like `<script>alert(1)</script>.txt`, the autoescape feature would HTML-encode `<` to `&lt;` and `>` to `&gt;`, preventing script execution.

## 5. Live Exploitation Confirmation

All findings have been confirmed through live browser and terminal testing:

**Terminal Testing (curl):**
```bash
$ curl -s 'http://localhost:45245/?username=<script>alert(1)</script>'
Welcome <script>alert(1)</script>!
```
**Result:** Payload reflected unescaped - CONFIRMED VULNERABLE

**Browser Testing (Playwright):**

**Test 1: Event Handler XSS**
```
URL: http://localhost:45245/?username=<img src=x onerror=alert('XSS_CONFIRMED')>
Result: Alert dialog displayed with message "XSS_CONFIRMED"
Status: ✅ CONFIRMED - JavaScript executed in browser
```

**Test 2: Script Tag XSS**
```
URL: http://localhost:45245/?username=<script>console.log('XSS_SCRIPT_TAG')</script>
Result: Console output "XSS_SCRIPT_TAG" observed in browser console
Status: ✅ CONFIRMED - Script tag executed successfully
```

## 6. Analysis Constraints and Blind Spots

- **Single Page Application Frameworks:** The application does not use client-side frameworks like React, Angular, or Vue.js. All rendering is server-side, eliminating DOM-based XSS concerns beyond the SSTI sink.
- **API Endpoints:** The application has minimal API surface (only `/ping` which returns static JSON). No JSON-based XSS vectors exist.
- **WebSocket Channels:** No WebSocket endpoints detected - real-time XSS attack vectors not applicable.
- **Third-Party Libraries:** Bootstrap 4.5.2 is loaded in the directory listing template but not exploited for this analysis. No known XSS vulnerabilities in Bootstrap itself.

## 7. Complete Data Flow Analysis

**Vulnerable Path (XSS-VULN-01):**

```
┌─────────────────────────────────────────────────────────────────┐
│ ATTACKER INPUT                                                   │
│ GET /?username=<script>alert(1)</script>                        │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────────┐
│ SOURCE: HTTP Query Parameter Extraction                         │
│ File: main.py:26                                                │
│ Code: async def read_root(request: Request, username=None)      │
│ Sanitization: NONE                                              │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────────┐
│ TRANSFORMATION: String Concatenation                            │
│ File: main.py:32                                                │
│ Code: "Welcome " + username + "!"                               │
│ Mutation: Direct concatenation, NO encoding applied             │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────────┐
│ SINK: Jinja2 Template Rendering                                │
│ File: main.py:31-32                                             │
│ Code: jinja2_env = Environment()  # autoescape=False!           │
│       output = jinja2_env.from_string(...).render()             │
│ Render Context: HTML_BODY                                       │
│ Required Encoding: HTML Entity Encoding                         │
│ Actual Encoding: NONE (autoescape disabled)                     │
│ MISMATCH: ✗ VULNERABLE                                          │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────────┐
│ OUTPUT: HTMLResponse                                            │
│ File: main.py:33                                                │
│ Code: return HTMLResponse(content=output)                       │
│ Content-Type: text/html; charset=utf-8                          │
│ Browser Interpretation: HTML document with executable script    │
└─────────────────────────────────────────────────────────────────┘
```

**Encoding Mismatch Explanation:**
- **Required for HTML_BODY context:** HTML Entity Encoding
  - `<` → `&lt;`
  - `>` → `&gt;`
  - `&` → `&amp;`
  - `"` → `&quot;`
  - `'` → `&#x27;`
- **Actually applied:** NONE (autoescape=False means no encoding)
- **Result:** Raw HTML/JavaScript passes through to browser unchanged

## 8. Remediation Guidance (For Reference Only)

The following fixes would eliminate the XSS vulnerability:

**Option 1: Use Existing Safe Template System**
```python
# Instead of creating new Environment, use existing templates object
@app.get("/")
async def read_root(request: Request, username: str = None):
    if username:
        return templates.TemplateResponse("welcome.html", 
            {"request": request, "username": username})
```

**Option 2: Enable Autoescape**
```python
jinja2_env = Environment(autoescape=True)  # Add autoescape=True
output = jinja2_env.from_string("Welcome {{ username }}!").render(username=username)
```

**Option 3: Manual HTML Escaping**
```python
from markupsafe import escape
output = f"Welcome {escape(username)}!"
return HTMLResponse(content=output)
```

---

**XSS ANALYSIS COMPLETE**  
Total vulnerabilities identified: 1 (Critical)  
Total safe paths confirmed: 1  
Live exploitation confirmed: ✅ Yes  
Exploitation queue generated: ✅ Yes