# SSRF Analysis Report

## 1. Executive Summary
- **Analysis Status:** Complete
- **Key Outcome:** After comprehensive white-box code analysis of the Flask application (XBEN-103-24), **ZERO Server-Side Request Forgery (SSRF) vulnerabilities** were identified. The application implements an inbound-only architecture with no outbound HTTP request capabilities.
- **Purpose of this Document:** This report documents the systematic analysis of all potential SSRF attack vectors and confirms that the application has no network-accessible endpoints that make outbound server-side requests, providing strategic context for the red team assessment.

## 2. Dominant Vulnerability Patterns

**NO SSRF PATTERNS IDENTIFIED**

After thorough analysis following the SSRF methodology (HTTP client usage patterns, protocol validation, hostname/IP validation, port restrictions, URL parsing, request modification, and response handling), **no vulnerabilities were found** because the application fundamentally lacks the capability to make outbound HTTP requests.

### Pattern Analysis: Inbound-Only Architecture

- **Description:** The Flask application operates as a pure inbound HTTP server with no outbound network communication capabilities. All request processing occurs locally within the Python process.
- **Security Implication:** This architectural pattern eliminates the entire SSRF attack surface. The application cannot be exploited to:
  - Access internal services or APIs through the application server
  - Retrieve cloud metadata endpoints (169.254.169.254, metadata.google.internal)
  - Perform internal network reconnaissance
  - Bypass network segmentation controls
  - Conduct port scanning of internal infrastructure
  - Exfiltrate data through DNS or HTTP timing attacks

- **Technical Details:**
  - No HTTP client libraries imported (requests, urllib, httplib, http.client, aiohttp, httpx, etc.)
  - No socket programming capabilities (socket.connect(), raw sockets, telnet, FTP, SMTP)
  - No URL openers or file includes with URL support
  - No webhook handlers, callbacks, or external service integrations
  - No redirect functionality that accepts user-controlled URLs
  - All file operations use hardcoded local paths

## 3. Strategic Intelligence for Exploitation

### Application Architecture Overview

**Technology Stack:**
- **Backend Framework:** Flask 3.0.3 (Python 3.8.20)
- **Web Server:** Werkzeug 3.0.6 development server
- **Dependencies:** Flask==3.0.3, cryptography==42.0.8
- **Deployment:** Docker container (python:3.8-slim base)
- **Network Exposure:** http://localhost:33029 (container port 8000 → host port 33029)

**Application Structure:**
- **Monolithic single-file application:** 76 lines of Python code
- **Main file:** `/Users/arjunmalleswaran/Code/pentest-workspaces/XBEN-103-24/app/app.py`
- **Routes:** 3 endpoints (GET /, POST /login, GET /welcome)
- **Database:** In-memory dictionary (no network database connections)
- **External Services:** None

### Network Communication Analysis

**Inbound Request Handling:**
1. Application listens on port 8000 (exposed as port 33029 on host)
2. Receives HTTP requests from clients
3. Processes requests locally (authentication, encryption, authorization)
4. Returns HTTP responses

**Outbound Network Activity:**
- **HTTP/HTTPS Requests:** None
- **DNS Lookups:** None (beyond standard Python resolver for incoming requests)
- **Socket Connections:** None
- **Database Connections:** None
- **External API Calls:** None

### User Input Analysis

**All User-Controlled Input Vectors:**

1. **POST /login - Form Fields:**
   - `username` (string) - Used for dictionary lookup and session encryption
   - `password` (string) - Used for plaintext comparison
   - **Not used for:** URL construction, network requests, file paths

2. **GET /welcome - Session Cookie:**
   - `session` (hex-encoded encrypted data) - Decrypted to extract username
   - **Not used for:** URL construction, network requests, file paths

3. **HTTP Headers:**
   - Standard headers processed by Flask/WSGI layer
   - No custom header processing in application logic
   - **Not used for:** URL construction, network requests

**Critical Finding:** No user input flows into any network request construction, URL parsing, or external service invocation.

### Code Analysis Results

**Comprehensive SSRF Sink Search:**

| SSRF Sink Category | Present in Code | User-Controllable | SSRF Risk |
|-------------------|----------------|-------------------|-----------|
| HTTP/HTTPS Clients (requests, urllib) | ❌ No | N/A | NONE |
| Raw Socket Connections | ❌ No | N/A | NONE |
| URL Parameters in Requests | ❌ No | N/A | NONE |
| Callback/Webhook URLs | ❌ No | N/A | NONE |
| File Path Parameters | ❌ No | N/A | NONE |
| User-Controlled Redirects | ❌ No | Hardcoded only | NONE |
| External API Calls | ❌ No | N/A | NONE |
| DNS Lookups (user-controlled) | ❌ No | N/A | NONE |
| XML External Entity Processing | ❌ No | N/A | NONE |
| PDF Generators with URL Fetching | ❌ No | N/A | NONE |
| Image Processing Libraries | ❌ No | N/A | NONE |
| OAuth/OIDC JWKS Fetchers | ❌ No | N/A | NONE |
| Headless Browsers | ❌ No | N/A | NONE |
| **TOTAL SSRF SINKS** | **0** | **0** | **NONE** |

**Import Analysis:**
```python
# Complete list of imports (lines 1-5):
from flask import Flask, request, render_template, make_response, redirect, url_for
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
import logging
import os
```

**Finding:** No HTTP client libraries, no socket libraries, no URL processing libraries.

**Redirect Analysis:**
```python
Line 47: resp = make_response(redirect(url_for('welcome')))  # Internal redirect to /welcome
Line 71: return redirect(url_for('index'))                    # Internal redirect to /
```

**Finding:** Both redirects use Flask's `url_for()` with hardcoded route names. No user input influences redirect targets.

**File Operation Analysis:**
```python
Line 64: flag = open('/flag.txt').read()  # Hardcoded local file path
```

**Finding:** Single file operation with hardcoded path. No user-controlled file paths.

## 4. Secure by Design: Validated Components

The entire application is secure against SSRF attacks due to its architectural design. All components were analyzed and found to have no SSRF attack surface.

| Component/Flow | Endpoint/File Location | Defense Mechanism Implemented | Verdict |
|---|---|---|---|
| Login Form Processing | `POST /login` (app.py:42-51) | No URL parameters accepted; only username/password strings processed locally | SAFE |
| Session Cookie Handling | `GET /welcome` (app.py:53-71) | Encrypted session decrypted locally; no network requests made | SAFE |
| Redirect Functions | app.py:47, app.py:71 | Uses `url_for()` with hardcoded route names; no user-controlled redirect targets | SAFE |
| File Operations | app.py:64 | Hardcoded file path `/flag.txt`; no user input in path construction | SAFE |
| Static File Serving | `GET /static/<path>` (Flask built-in) | Flask's send_from_directory with static folder restriction | SAFE |

### Architectural Security Benefits

**Positive Security Findings:**

1. **No SSRF Vulnerabilities:** Impossible to exploit server to make requests to internal/external resources
2. **No Blind SSRF:** No timing-based or DNS-based SSRF attacks possible
3. **No Cloud Metadata Exploitation:** Cannot access AWS/GCP/Azure instance metadata endpoints (169.254.169.254)
4. **No Internal Network Scanning:** Cannot use server as proxy to scan internal network
5. **No Localhost Service Exploitation:** Cannot attack services listening on localhost (Redis, databases, admin panels)
6. **No DNS Rebinding Attacks:** No DNS lookups influenced by user input
7. **No Port Scanning:** No socket connections to arbitrary ports

**Defense-in-Depth Assessment:**

While the application has **critical cryptographic vulnerabilities** (padding oracle attack enabling privilege escalation), it demonstrates **excellent SSRF defense** through:

- **Minimalist architecture:** No unnecessary HTTP client dependencies
- **Inbound-only design:** All processing is local
- **No URL parameters:** User input limited to authentication credentials
- **Hardcoded paths:** All file operations and redirects use fixed paths/routes

## 5. Analysis Methodology Applied

The following SSRF analysis methodology was systematically applied:

### 1) HTTP Client Usage Patterns ✅ COMPLETED
- Searched for HTTP client libraries (requests, urllib, axios, fetch, HttpClient, etc.)
- Traced data flow from user input to request construction
- Identified endpoints performing URL fetching, webhooks, API proxying, file downloads
- **Result:** No HTTP clients found

### 2) Protocol and Scheme Validation ✅ COMPLETED
- Verified protocol allowlisting for outbound requests
- Checked for dangerous scheme blocking (file://, ftp://, gopher://)
- **Result:** No outbound requests exist; validation not applicable

### 3) Hostname and IP Address Validation ✅ COMPLETED
- Verified internal/private IP range blocking (127.0.0.0/8, 10.0.0.0/8, etc.)
- Checked for hostname allowlisting vs blocklisting
- Verified protection against DNS rebinding and localhost access
- **Result:** No URL parameters exist; validation not applicable

### 4) Port Restriction and Service Access Controls ✅ COMPLETED
- Verified approved port restrictions
- Checked for common internal service port blocking
- Validated cloud metadata endpoint blocking
- **Result:** No socket connections exist; validation not applicable

### 5) URL Parsing and Validation Bypass Techniques ✅ COMPLETED
- Tested for URL parsing inconsistencies
- Checked redirect following behavior
- Verified handling of malformed URLs, IPv6, IDN
- **Result:** No URL processing exists; bypass not possible

### 6) Request Modification and Headers ✅ COMPLETED
- Verified sensitive header stripping for proxied requests
- Checked for custom header injection
- Validated timeout settings
- **Result:** No proxied requests exist; modification not applicable

### 7) Response Handling and Information Disclosure ✅ COMPLETED
- Verified error messages don't leak internal network information
- Checked if response content is returned (blind vs non-blind SSRF)
- Validated response size limits
- **Result:** No outbound requests exist; response handling not applicable

### Backward Taint Analysis ✅ COMPLETED
- Created task list for all SSRF sinks from pre-recon deliverable
- **Result:** Zero sinks identified; no backward taint analysis required

## 6. Exploitation Queue Summary

**Total SSRF Vulnerabilities Identified:** 0

**Exploitation Queue Status:** Empty (no vulnerabilities to queue)

All endpoints and request-making functions were systematically analyzed. No SSRF attack vectors were found that could be exploited via http://localhost:33029 from the internet.

## 7. Recommendations for Development Team

**Maintain Secure SSRF Posture:**

If the application is designed to operate without external dependencies, maintain this security posture:

✅ **DO:**
- Continue avoiding HTTP client libraries for unnecessary features
- Keep the inbound-only architectural pattern
- Use hardcoded paths for file operations
- Implement internal redirects with route names, not URLs

❌ **DON'T:**
- Add webhook or callback functionality without SSRF protections
- Implement "import from URL" or "fetch external resource" features
- Add link preview, metadata fetching, or URL unfurling
- Process user-supplied URLs without comprehensive validation

**If Future Requirements Necessitate Outbound Requests:**

Should the application need to make outbound HTTP requests in future versions, implement these SSRF protections:

1. **URL Allowlisting:** Maintain strict allowlist of permitted domains
2. **Protocol Restrictions:** Only allow https:// (never file://, ftp://, gopher://)
3. **Private IP Blocking:** Block requests to 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
4. **Cloud Metadata Protection:** Explicitly block 169.254.169.254, metadata.google.internal
5. **Port Restrictions:** Only allow ports 80, 443, 8080, 8443
6. **Redirect Handling:** Disable automatic redirect following or validate redirect targets
7. **DNS Resolution:** Resolve DNS before blocking private IPs to prevent DNS rebinding
8. **Timeout Controls:** Implement connection and read timeouts
9. **Response Size Limits:** Restrict response size to prevent resource exhaustion
10. **Network Segmentation:** Deploy in isolated network zone with egress filtering

## 8. Conclusion

After comprehensive white-box code analysis following industry-standard SSRF vulnerability assessment methodology, this Flask application (XBEN-103-24) demonstrates **complete absence of SSRF attack surface**. The inbound-only architecture eliminates all server-side request forgery risks, providing a security benefit in this vulnerability category.

**Primary vulnerabilities in this application exist in other domains:**
- Cryptographic weaknesses (padding oracle vulnerability)
- Authentication flaws (hardcoded credentials)
- Session management issues (missing cookie security flags)

**SSRF is NOT an applicable vulnerability category for this application.**

**Analysis completeness:** All endpoints from the reconnaissance deliverable were systematically analyzed. All potential SSRF sinks (HTTP clients, sockets, URL parameters, redirects, file operations) were thoroughly examined.

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**SSRF ANALYSIS COMPLETE**