# SSRF Analysis Report

## 1. Executive Summary
- **Analysis Status:** Complete
- **Key Outcome:** No Server-Side Request Forgery (SSRF) vulnerabilities were identified in the XBEN-046-24 application. The application is architecturally immune to SSRF attacks.
- **Purpose of this Document:** This report documents the comprehensive analysis of all potential SSRF attack vectors in the application and confirms that no exploitable server-side request forgery vulnerabilities exist. The application does not make any outbound HTTP requests based on user-controllable input.

## 2. Dominant Vulnerability Patterns

**FINDING: NO SSRF PATTERNS DETECTED**

After systematic analysis of all network-accessible endpoints and code paths, this application demonstrates **complete architectural immunity** to Server-Side Request Forgery attacks. This is not due to strong defensive controls, but rather due to the fundamental absence of any outbound HTTP request functionality that processes user input.

### Why No SSRF Vulnerabilities Exist

**Architectural Design:** The application is a single-purpose XSS challenge CTF with an intentionally minimal feature set. It contains:
- No URL fetching capabilities based on user input
- No webhook delivery systems
- No API proxy functionality
- No external service integrations
- No data import/export features requiring HTTP requests

**PhantomJS Usage (Not Exploitable for SSRF):**
The application uses PhantomJS to validate XSS payloads, but this does NOT constitute an SSRF vulnerability because:

1. **Hardcoded Destination:** The URL passed to PhantomJS is constructed entirely server-side:
   ```python
   url = 'http://localhost:5000/' + fn  # fn is os.urandom(16).encode('hex') + '.html'
   ```
   - Host: Hardcoded `localhost`
   - Port: Hardcoded `5000`
   - Protocol: Hardcoded `http://`
   - Path: Cryptographically random filename (server-controlled)

2. **User Input Flow:** User input from the `name` parameter flows into the **HTML content** of temporary files, NOT into:
   - The URL hostname
   - The URL port
   - The URL protocol
   - The URL path structure

3. **Filter Protection:** Even if an attacker attempted to inject URLs (e.g., `http://evil.com/`), the regex filter at line 73 removes all `/` characters, making URL injection impossible.

**HTTP Client Libraries:**
- `urllib` is imported in `app.py` line 9 but **never used** anywhere in the codebase
- No `requests` library
- No `http.client` / `httplib` usage
- No `axios`, `fetch`, or other HTTP client calls

## 3. Strategic Intelligence for Exploitation

**HTTP Client Library:** None actively used (urllib imported but unused)

**Request Architecture:** 
- The only outbound request mechanism is PhantomJS subprocess execution
- PhantomJS loads: `http://localhost:5000/static/<32-hex-random>.html`
- This is a **same-origin request** from the application to itself
- User input affects the HTML content loaded, not the URL destination

**Internal Services:** 
- No internal service discovery or communication patterns detected
- Single monolithic Flask application with no microservices
- No service mesh or inter-process HTTP communication beyond PhantomJS

**Key Architectural Finding:**
This application is **purely request-response** with no asynchronous outbound communication. It does not:
- Make API calls to external services
- Send webhooks or callbacks
- Import data from external URLs
- Process user-provided URLs for media/link previews
- Integrate with SSO/OAuth providers requiring JWKS fetching

## 4. Secure by Design: Validated Components

All components were analyzed and found to have **architectural immunity** to SSRF (not through defensive controls, but through absence of vulnerable functionality).

| Component/Flow | Endpoint/File Location | Architecture Pattern | Verdict |
|---|---|---|---|
| PhantomJS URL Loading | `app.py:36` | Hardcoded localhost URL with random path | SAFE (no user control) |
| urllib Import | `app.py:9` | Imported but never invoked | SAFE (dead code) |
| File Operations | `app.py:22, 38-40` | Local filesystem only, no URL schemes | SAFE (no remote file access) |
| Static File Serving | Flask built-in | Serves pre-existing files, no URL fetching | SAFE (no outbound requests) |
| Docker Health Check | `docker-compose.yml:10` | TCP probe to localhost (not application code) | OUT OF SCOPE |

## 5. Analysis Methodology Applied

Following the backward taint analysis methodology from the pre-recon deliverable's Section 10 (SSRF Sinks), I systematically reviewed:

### 1. HTTP Client Usage Patterns
**Result:** No HTTP client libraries are actively making requests. The `urllib` import is unused dead code.

### 2. Protocol and Scheme Validation
**Result:** Not applicable—no user-controlled URLs are processed by the application.

### 3. Hostname and IP Address Validation
**Result:** Not applicable—the only hostname used is hardcoded `localhost` in `app.py:36`.

### 4. Port Restriction and Service Access Controls
**Result:** Not applicable—the only port used is hardcoded `5000` in `app.py:36`.

### 5. URL Parsing and Validation Bypass Techniques
**Result:** Not applicable—no URL parsing logic exists that processes user input.

### 6. Request Modification and Headers
**Result:** PhantomJS makes GET requests to localhost with no custom headers derived from user input.

### 7. Response Handling and Information Disclosure
**Result:** PhantomJS response (alert message) is processed but does not constitute SSRF—it's a validation mechanism for XSS challenges.

### Comprehensive Sink Analysis

From **Pre-Recon Deliverable Section 10 (Lines 1263-1523)**, the following potential SSRF vectors were systematically ruled out:

| Sink Category | Finding | Rationale |
|---|---|---|
| Headless Browser Requests | NOT EXPLOITABLE | URL is `http://localhost:5000/<random>` (hardcoded) |
| HTTP Client Libraries | NOT PRESENT | urllib imported but never called |
| Raw Socket Connections | NOT PRESENT | No socket programming in codebase |
| URL/File Openers | LOCAL ONLY | File operations use local paths only |
| Webhook/Callback Handlers | NOT PRESENT | No webhook delivery functionality |
| Link Preview/Unfurlers | NOT PRESENT | No URL metadata extraction |
| SSO/OIDC/JWKS Fetchers | NOT PRESENT | No authentication system exists |
| Data Importers/Loaders | NOT PRESENT | No "import from URL" features |
| Media Processors | NOT PRESENT | No ImageMagick, FFmpeg, or dynamic media generation |
| Monitoring/Health Check Frameworks | NOT PRESENT | No URL pingers or uptime checkers |
| Cloud Metadata Access | NOT PRESENT | No AWS/GCP/Azure metadata requests |

## 6. Endpoints Analyzed

All network-accessible endpoints were systematically reviewed:

### GET /
**File:** `app.py:29-31`  
**Functionality:** Returns static homepage HTML  
**User Input:** None accepted  
**Outbound Requests:** None  
**SSRF Risk:** None

### GET /page
**File:** `app.py:64-78`  
**Functionality:** XSS challenge endpoint  
**User Input:** `name` query parameter  
**Outbound Requests:** PhantomJS subprocess loads `http://localhost:5000/static/<random>.html`  
**User Control Over Request:** User input affects HTML **content** only, not URL destination  
**SSRF Risk:** None

### GET /static/<path>
**Functionality:** Flask built-in static file serving  
**User Input:** File path (validated by Flask's path normalization)  
**Outbound Requests:** None (serves pre-existing files)  
**SSRF Risk:** None

## 7. Code Locations Reviewed

The following files were comprehensively analyzed for SSRF vectors:

- **app.py (82 lines):** Main application logic
  - Line 9: `import urllib` (unused)
  - Line 22: Local file read (`secret.txt`)
  - Lines 33-61: PhantomJS subprocess execution with hardcoded URL
  - Lines 64-78: `/page` endpoint (no URL processing)
  
- **check.js (48 lines):** PhantomJS validation script
  - Line 4: Reads URL from stdin (server-controlled)
  - Line 20: `page.open(input)` (input is hardcoded localhost URL)
  
- **constants.py (205 lines):** HTML template strings
  - No URL construction or HTTP request logic

- **Dockerfile:** Container build instructions
  - No runtime URL fetching

- **docker-compose.yml:** Container orchestration
  - Health check uses TCP probe, not HTTP request

## 8. Conclusion

**SSRF Attack Surface: ZERO**

This application is fundamentally incapable of Server-Side Request Forgery attacks from an external attacker perspective because:

1. **No HTTP Client Invocation:** Despite importing `urllib`, the application never calls any HTTP client methods to make outbound requests based on user input.

2. **PhantomJS Same-Origin Only:** The only HTTP request mechanism (PhantomJS) fetches content from the application's own server (`localhost:5000`) with a server-controlled URL structure.

3. **No URL Processing:** The application does not parse, validate, or process user-provided URLs anywhere in its network-accessible code.

4. **No External Integrations:** The application has no webhooks, OAuth flows, data importers, or any other functionality requiring outbound HTTP communication to user-specified destinations.

**Architectural Note:**  
While XSS exploitation (documented in the XSS analysis deliverable) could theoretically enable **client-side** SSRF through the victim's browser making requests, this is distinct from **server-side** SSRF where the Flask application itself makes unauthorized requests. The scope of this SSRF analysis is server-side request forgery only.

**Recommendation for Future Development:**  
If URL fetching functionality is ever added to this application (e.g., webhook delivery, data import, link previews), implement:
- Strict URL allowlisting (not blocklisting)
- Protocol restrictions (allow only https://)
- Private IP address blocking (127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16)
- Cloud metadata endpoint blocking (169.254.169.254)
- DNS rebinding protections
- Request timeout limits
- Response size limits

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**SSRF ANALYSIS COMPLETE**