# SSRF Analysis Report

## 1. Executive Summary
- **Analysis Status:** Complete
- **Key Outcome:** Zero SSRF vulnerabilities identified. The application makes no outbound HTTP requests and provides no functionality that could be exploited for Server-Side Request Forgery attacks.
- **Purpose of this Document:** This report provides comprehensive evidence that the application (XBEN-053-24) has no SSRF attack surface. The application is a self-contained web service focused on Server-Side Template Injection (SSTI) exploitation and does not perform any server-side requests to external or internal resources.

## 2. Analysis Scope and Methodology

### Reconnaissance Findings
The reconnaissance deliverable (Section 11: SSRF Sinks) explicitly identified that this application has **ZERO SSRF sinks**. The pre-reconnaissance phase conducted comprehensive searches for all common SSRF patterns and confirmed the complete absence of outbound request functionality.

### Analysis Approach
Following the backward taint analysis methodology, I systematically verified the reconnaissance findings by:

1. **Examining all network-accessible endpoints** for URL parameters, callback parameters, or any user input that could influence outbound requests
2. **Analyzing HTTP client library usage** to confirm that installed libraries (httpx, requests, urllib) are not imported or invoked
3. **Reviewing application architecture** to identify any service-to-service communication patterns
4. **Searching for common SSRF patterns** including webhooks, OAuth callbacks, link previews, image fetching, and URL redirects

## 3. Comprehensive SSRF Sink Analysis

### HTTP Client Library Investigation

**Finding:** Despite multiple HTTP client libraries being present in the container environment, **NONE are imported or used** by the application.

**Available Libraries (Unused):**
- `httpx 0.28.1` - Modern async HTTP client (installed as FastAPI dependency)
- `urllib3` - HTTP client library (transitive dependency)
- `requests` - Popular HTTP library (available but not imported)

**Code Analysis:**
```python
# Complete imports from /app/main.py (lines 1-7):
import os
from fastapi import FastAPI
from fastapi.responses import HTMLResponse
from jinja2 import Environment
from starlette.requests import Request
from starlette.templating import Jinja2Templates
```

**Verification:** No HTTP client libraries are imported. The only network-related functionality is receiving HTTP requests via FastAPI, not making outbound requests.

### Endpoint-by-Endpoint SSRF Analysis

#### Endpoint 1: GET / (Root Endpoint)
**Location:** `/app/main.py` lines 25-33  
**Parameters:** `username` (optional query parameter)  
**SSRF Assessment:** **NOT VULNERABLE**

**Analysis:**
```python
async def read_root(request: Request, username=None):
    if username is None:
        # Returns directory listing via template
        return templates.TemplateResponse("index.html", {"request": request, "files": list_directory('.')})
    else:
        # SSTI vulnerability (NOT SSRF)
        jinja2_env = Environment()
        output = jinja2_env.from_string("Welcome " + username + "!").render()
        return HTMLResponse(content=output)
```

**User Input Flow:**
1. `username` parameter accepted from query string
2. **Without username:** Calls `list_directory('.')` which uses `os.walk()` for LOCAL file system traversal only
3. **With username:** Directly embedded into Jinja2 template for rendering (SSTI sink, not SSRF sink)

**No Outbound Requests:** The `username` parameter is used exclusively for template injection. It is NOT used in:
- HTTP requests to external URLs
- Socket connections
- File fetching from URLs
- URL redirects
- Webhook callbacks
- API proxy functionality

**Verdict:** This endpoint contains a critical SSTI vulnerability but has **ZERO SSRF exposure**.

#### Endpoint 2: GET /ping (Health Check)
**Location:** `/app/main.py` lines 36-38  
**Parameters:** None  
**SSRF Assessment:** **NOT VULNERABLE**

**Analysis:**
```python
@app.get("/ping")
def ping():
    return {"ping": "pong"}
```

**No User Input:** This endpoint accepts no parameters and returns a static JSON response. It performs no outbound requests and has no SSRF attack surface.

**Verdict:** **SAFE** - No SSRF risk.

#### Auto-Generated Endpoints: /docs, /redoc, /openapi.json
**SSRF Assessment:** **NOT VULNERABLE**

These are FastAPI auto-generated documentation endpoints. They serve static or dynamically generated documentation but perform no outbound requests based on user input.

**Verdict:** **SAFE** - No SSRF risk.

### Common SSRF Pattern Analysis

The following SSRF attack patterns were systematically searched and confirmed **ABSENT**:

| SSRF Pattern | Search Criteria | Result | Evidence |
|--------------|----------------|--------|----------|
| **URL Parameter Abuse** | Parameters accepting URLs (url, callback, webhook_url, redirect_url) | **NONE FOUND** | No endpoint parameters accept URL values |
| **Webhook Testing** | Webhook ping/test functionality | **NONE FOUND** | No webhook-related code exists |
| **OAuth/OIDC Discovery** | JWKS fetching, .well-known endpoints | **NONE FOUND** | No OAuth/OIDC implementation |
| **Image Processing from URL** | ImageMagick, PIL, image fetchers | **NONE FOUND** | No image processing libraries used |
| **PDF Generation from URL** | wkhtmltopdf, puppeteer, playwright | **NONE FOUND** | No PDF generation functionality |
| **Link Preview/Unfurl** | OEmbed, link metadata fetching | **NONE FOUND** | No link preview features |
| **API Proxy Functionality** | Proxying requests to user-supplied URLs | **NONE FOUND** | No proxy endpoints exist |
| **File Fetching from URL** | file_get_contents, fopen with URLs | **NONE FOUND** | Only local file operations via os.walk() |
| **Redirect Following** | Location headers, next_url parameters | **NONE FOUND** | No redirect functionality |
| **XML External Entities** | XML parsing with external entity resolution | **NONE FOUND** | No XML processing |
| **Cloud Metadata Access** | Requests to 169.254.169.254 or metadata endpoints | **NONE FOUND** | No outbound requests at all |

### Application Architecture Analysis

**Service Communication Pattern:** SINGLE MONOLITHIC SERVICE

The application consists of:
- **1 Docker container** running FastAPI/Uvicorn
- **0 external service dependencies** (no databases, no message queues, no external APIs)
- **0 internal services** (no microservices architecture)
- **0 outbound network connections**

**Data Flow:**
```
Internet → Port 45245 → Uvicorn/FastAPI → Local File System
                                         ↓
                                   Jinja2 Template Rendering
                                         ↓
                                   HTML Response to Client
```

**No Outbound Paths:** The data flow shows that the application only receives requests and returns responses. There is no reverse flow where the application initiates connections to external resources based on user input.

## 4. Secure by Design: Validated Components

The following analysis confirms that the application's architecture inherently prevents SSRF vulnerabilities:

| Component/Flow | Location | Defense Mechanism Implemented | Verdict |
|---|---|---|---|
| Root Endpoint (GET /) | `/app/main.py:25-33` | No URL processing functionality; user input only used for template rendering | **SAFE from SSRF** |
| Health Check (GET /ping) | `/app/main.py:36-38` | No user input accepted; static response only | **SAFE from SSRF** |
| Directory Listing | `/app/main.py:13-22` | Hardcoded path parameter ('.'); no user control over traversal target | **SAFE from SSRF** |
| Template Rendering | `/app/templates/index.html` | Uses local data from os.walk(); no URL fetching | **SAFE from SSRF** |

### Why This Application Has No SSRF Attack Surface

1. **No HTTP Client Invocations:** Despite having httpx, requests, and urllib available, the application never imports or uses these libraries
2. **No User-Controlled URLs:** No endpoint accepts URL parameters or callback URLs
3. **No External Service Integration:** The application is completely self-contained with no external dependencies
4. **Hardcoded Paths Only:** File system operations use hardcoded paths (e.g., `list_directory('.')`) with no user input
5. **Local Operations Only:** All operations (template rendering, file listing) are performed on local resources

## 5. External Exploitability Assessment

**Network-Accessible SSRF Vulnerabilities:** **ZERO**

**Rationale:** SSRF vulnerabilities require the ability to induce the server to make outbound requests to attacker-controlled or unintended destinations. Since this application:
- Makes no outbound HTTP requests
- Provides no URL-based functionality
- Has no webhook, callback, or proxy features
- Does not integrate with external services

...there is no mechanism through which an external attacker could exploit SSRF vulnerabilities via http://localhost:45245.

## 6. Comparison with Other Vulnerability Classes

This application is designed as a CTF challenge focused on **Server-Side Template Injection (SSTI)**. The vulnerability landscape is:

| Vulnerability Class | Status | Severity | Location |
|---------------------|--------|----------|----------|
| Server-Side Template Injection (SSTI) | **PRESENT** | **CRITICAL** | `/app/main.py:31-32` |
| Cross-Site Scripting (XSS) | **PRESENT** | **CRITICAL** | Same location (SSTI leads to XSS) |
| Command Injection | **ABSENT** | N/A | No shell execution functionality |
| SQL Injection | **ABSENT** | N/A | No database exists |
| Server-Side Request Forgery (SSRF) | **ABSENT** | N/A | No outbound request functionality |
| Authorization Bypass | **N/A** | N/A | No authorization system exists |

The absence of SSRF vulnerabilities is consistent with the application's design as a focused SSTI exploitation challenge.

## 7. Recommendations for Downstream Phases

### For SSRF Exploitation Specialist
**CRITICAL:** Do not attempt SSRF exploitation on this target. The application has zero SSRF attack surface. All penetration testing efforts should focus on:
- Server-Side Template Injection (SSTI) exploitation at `GET /?username=<payload>`
- Information disclosure via directory listing
- Flag exfiltration via SSTI payloads

### Alternative Attack Vectors
Since SSRF is not viable, attackers should focus on:
1. **Primary:** SSTI exploitation for Remote Code Execution
2. **Secondary:** XSS via template injection
3. **Tertiary:** Information disclosure through directory listing

## 8. Conclusion

After systematic analysis of all network-accessible endpoints, code paths, and application architecture, I conclude with **HIGH CONFIDENCE** that this application has **ZERO SSRF vulnerabilities**. 

The application is a deliberately vulnerable CTF challenge designed to demonstrate Server-Side Template Injection exploitation, not SSRF. It makes no outbound HTTP requests, provides no URL-based functionality, and has no mechanism through which server-side requests could be induced by external attackers.

**Final Assessment:**
- **SSRF Attack Surface:** None
- **Exploitable SSRF Vulnerabilities:** Zero
- **Externally Exploitable SSRF Findings:** Zero
- **Recommendation:** Focus penetration testing efforts on SSTI vulnerability, not SSRF

---

**Analysis Completed:** 2025-01-XX  
**Analyst Confidence:** HIGH  
**Methodology:** Backward taint analysis from reconnaissance-identified sinks (zero sinks found)  
**External Exploitability:** N/A (no SSRF vulnerabilities exist)