# SSRF Analysis Report

## 1. Executive Summary

- **Analysis Status:** Complete
- **Key Outcome:** No Server-Side Request Forgery (SSRF) vulnerabilities were identified in the XBEN-004-24 "Dalgona Challenge" application. A comprehensive white-box analysis was conducted on all network-accessible endpoints, HTTP client usage patterns, and outbound request mechanisms.
- **Purpose of this Document:** This report provides the strategic context on the application's outbound request mechanisms (or lack thereof), systematic analysis of all potential SSRF vectors, and confirmation that no exploitable SSRF vulnerabilities exist in the network attack surface accessible via `http://localhost:5000/`.

## 2. Dominant Vulnerability Patterns

### No SSRF Patterns Identified

After systematic analysis of all network-accessible components, **ZERO SSRF vulnerability patterns were discovered**. The application demonstrates the following security characteristics:

**Pattern 1: No HTTP Client Usage**
- **Description:** Despite importing `urllib` (line 9 of src/app.py), the application makes ZERO HTTP requests to external or internal services. No HTTP client methods are invoked anywhere in the codebase.
- **Implication:** Without HTTP client calls, there is no mechanism for user input to influence outbound requests.
- **Code Evidence:** Comprehensive grep analysis found no `urlopen()`, `requests.get()`, `httplib` usage, or similar patterns.

**Pattern 2: Hardcoded PhantomJS URLs**
- **Description:** The application uses PhantomJS headless browser to render user-supplied HTML, but the URL loaded by PhantomJS is entirely server-controlled with hardcoded scheme, host, port, and cryptographically random filename.
- **Implication:** User input controls HTML content but cannot manipulate the URL destination, preventing SSRF exploitation.
- **Code Evidence:** `url = 'http://localhost:5000/' + fn` where `fn = "static/" + os.urandom(16).encode('hex') + '.html'` (lines 35-36 of src/app.py).

**Pattern 3: No URL Parameters Accepted**
- **Description:** The application accepts only one user input parameter (`solution` via POST form), which is designed for XSS exploitation, not URL-based operations. No parameters named `url`, `callback`, `webhook`, `redirect`, or similar exist.
- **Implication:** No user-controllable input channel exists for injecting malicious URLs.
- **Code Evidence:** Single input vector at line 62: `msg = request.form.get('solution','')`.

**Pattern 4: Zero Redirect/Webhook/Callback Functionality**
- **Description:** The application has no redirect handlers, no webhook testing endpoints, no OAuth/OIDC discovery mechanisms, and no external API integrations.
- **Implication:** No architectural components exist that could be exploited for SSRF.
- **Code Evidence:** Despite importing `redirect` and `url_for`, neither is used in the codebase.

## 3. Strategic Intelligence for Exploitation

**HTTP Client Library:** None actively used. `urllib` is imported but never invoked.

**Request Architecture:** 
- The application is a simple Flask monolith with only two routes: `GET /` (landing page) and `GET/POST /challenge` (XSS challenge).
- Outbound requests are limited to PhantomJS making HTTP requests to `http://localhost:5000/static/[random].html` to validate XSS payloads.
- All PhantomJS requests target hardcoded localhost URLs with server-generated filenames.

**Internal Services:** 
- PhantomJS subprocess runs on the same container as the Flask application
- PhantomJS accesses the Flask application via `http://localhost:5000/static/*`
- No other internal services, databases, or microservices exist
- No access to cloud metadata endpoints (169.254.169.254)
- No access to internal network ranges (10.x, 172.x, 192.168.x)

**PhantomJS Integration Details:**
- **Subprocess Invocation:** `subprocess.Popen(["timeout","5","phantomjs", "check.js"], ...)` (line 34)
- **URL Communication:** URL passed via stdin pipe: `proc.stdin.write(url)` (line 41)
- **PhantomJS Script:** `check.js` reads stdin and calls `page.open(input, ...)` (lines 4, 20)
- **Security Control:** 5-second timeout prevents infinite loops; array-based subprocess arguments prevent command injection

**Backward Taint Analysis - PhantomJS URL:**
```
Source: os.urandom(16) [cryptographically random bytes]
  ↓
fn = "static/" + os.urandom(16).encode('hex') + '.html'
  ↓
url = 'http://localhost:5000/' + fn [hardcoded scheme/host/port]
  ↓
proc.stdin.write(url) [passed to PhantomJS]
  ↓
Sink: page.open(input) in check.js

USER INPUT FLOW (SEPARATE PATH):
Source: request.form.get('solution','')
  ↓
Embedded in HTML template via string formatting
  ↓
Written to file as CONTENT: open(fn, 'w').write(page)
  ↓
PhantomJS renders the HTML content from the hardcoded localhost URL

VERDICT: User input controls CONTENT, not URL destination → NO SSRF
```

## 4. Secure by Design: Validated Components

These components were analyzed and found to have NO SSRF vulnerabilities. They represent secure implementation patterns (or intentional design choices that prevent SSRF).

| Component/Flow | Endpoint/File Location | Defense Mechanism Implemented | Verdict |
|---|---|---|---|
| PhantomJS URL Construction | `src/app.py` lines 35-36 | URL entirely server-controlled: hardcoded `http://localhost:5000/` + cryptographically random filename (`os.urandom(16)`). User input isolated to HTML content only. | SAFE |
| HTTP Client Usage | `src/app.py` line 9 (import) | Despite importing `urllib`, ZERO HTTP client methods are invoked. No `urlopen()`, `requests.get()`, or similar calls exist in codebase. | SAFE |
| File Operations | `src/app.py` lines 22, 38 | All file paths are hardcoded (`secret.txt`) or server-generated (random hex filenames). No user input in `open()` calls. | SAFE |
| Static File Serving | Flask default `/static/*` handler | Serves CSS, images, fonts, and temporary HTML files. No URL-based file fetching; all files are local filesystem access. | SAFE |
| Subprocess Execution | `src/app.py` line 34 | Array-based arguments prevent command injection: `["timeout","5","phantomjs","check.js"]`. No user input in command arguments. | SAFE |
| Redirect Handlers | N/A - None exist | Despite importing `redirect()` and `url_for()`, neither is used anywhere in the codebase. Zero redirect functionality. | SAFE |
| Webhook/Callback Testing | N/A - None exist | No endpoints accept webhook URLs, callback URLs, or external service integrations. Application is completely isolated. | SAFE |
| Authentication/SSO/OIDC | N/A - None exist | No authentication system exists, therefore no OAuth discovery endpoints, JWKS fetchers, or SSO redirect flows that could be exploited for SSRF. | SAFE |

## 5. Systematic Analysis Summary

### Methodology Applied

Per the SSRF analysis methodology, the following checks were performed systematically:

**1) Identify HTTP Client Usage Patterns:** ✅ COMPLETE
- **Result:** `urllib` imported but NEVER used; no `requests`, `httplib`, or other HTTP client libraries found
- **Endpoints analyzed:** `GET /`, `GET/POST /challenge`
- **URL parameters checked:** NONE found (only `solution` form parameter exists for XSS)

**2) Protocol and Scheme Validation:** ✅ N/A (No User-Controlled URLs)
- **Result:** PhantomJS uses hardcoded `http://` scheme
- **User input impact:** NONE - users cannot inject `file://`, `ftp://`, `gopher://`, or other dangerous schemes

**3) Hostname and IP Address Validation:** ✅ N/A (No User-Controlled URLs)
- **Result:** PhantomJS uses hardcoded `localhost` hostname
- **User input impact:** NONE - users cannot specify internal IPs (127.x, 10.x, 172.16.x, 192.168.x, 169.254.x) or external domains

**4) Port Restriction and Service Access Controls:** ✅ N/A (No User-Controlled URLs)
- **Result:** PhantomJS uses hardcoded port `5000`
- **User input impact:** NONE - users cannot access alternate ports (22, 23, 135, 445, etc.) or cloud metadata endpoints

**5) URL Parsing and Validation Bypass Techniques:** ✅ N/A (No User-Controlled URLs)
- **Result:** No URL parsing or validation exists because no user-controlled URLs are processed
- **Redirect following:** PhantomJS may follow HTML-based redirects in rendered content, but this is XSS, not SSRF

**6) Request Modification and Headers:** ✅ N/A (No Proxied Requests)
- **Result:** Application does not proxy external requests or forward user-supplied headers

**7) Response Handling and Information Disclosure:** ✅ COMPLETE
- **Result:** PhantomJS execution results return "SUCCESS" or failure messages, but do not disclose response content from external URLs (since no external URLs are fetched)

### Vectors Analyzed and Confirmed Secure

| Attack Vector | Analysis Result | Evidence |
|---|---|---|
| HTTP Client URL Injection | NOT APPLICABLE | No HTTP client calls exist despite urllib import |
| PhantomJS URL Control | SAFE | URL is `'http://localhost:5000/' + os.urandom(16).encode('hex') + '.html'` - entirely server-controlled |
| URL Query Parameters | NOT APPLICABLE | No `request.args.get()` calls; application uses only POST form data |
| Redirect Manipulation | NOT APPLICABLE | No `redirect()` or `url_for()` usage; no redirect endpoints exist |
| Webhook/Callback Testing | NOT APPLICABLE | No webhook testing endpoints exist |
| File Fetching from URLs | NOT APPLICABLE | All `open()` calls use hardcoded or server-generated local paths |
| Iframe src Injection | NOT APPLICABLE | `PAGE_CONTENT_IFRAME` template exists but is NEVER used (dead code) |
| OAuth/OIDC Discovery | NOT APPLICABLE | No authentication system exists |
| SSRF via XSS | LOW RISK | Users can inject HTML with `<meta http-equiv="refresh">` or JavaScript redirects, but these execute client-side in PhantomJS (XSS impact, not traditional SSRF) |

## 6. Detailed Backward Taint Analysis: PhantomJS Integration

### Sink Identification
**SINK:** `page.open(input)` in `src/check.js` line 20

### Backward Trace

**Step 1:** Identify where `input` originates
- `src/check.js` line 4: `var input = system.stdin.readLine();`
- Value comes from stdin, which is written by the Flask application

**Step 2:** Trace stdin write operation
- `src/app.py` line 41: `proc.stdin.write(url)`
- The `url` variable is written to stdin

**Step 3:** Trace `url` variable construction
- `src/app.py` line 36: `url = 'http://localhost:5000/' + fn`
- Components:
  - `'http://localhost:5000/'` - HARDCODED string literal
  - `fn` - Variable defined on line 35

**Step 4:** Trace `fn` variable construction
- `src/app.py` line 35: `fn = "static/" + os.urandom(16).encode('hex') + '.html'`
- Components:
  - `"static/"` - HARDCODED string literal
  - `os.urandom(16).encode('hex')` - CRYPTOGRAPHICALLY RANDOM 32 hex characters
  - `'.html'` - HARDCODED string literal

**Step 5:** Check for user input influence
- `os.urandom(16)` sources from operating system entropy pool - NO user control
- No concatenation with user input variables
- User input (`request.form.get('solution')`) flows into HTML content (line 72), NOT into `fn` or `url`

### Sanitization Analysis
**No sanitization required** - The entire URL construction path is server-controlled with no user input.

### Vulnerability Assessment
**VERDICT:** SAFE - No user input reaches the SSRF sink. The URL passed to `page.open()` is entirely server-controlled.

### Confidence Level
**HIGH (95%)** - The code path is deterministic with no user input influence. The 5% margin accounts for:
- Potential PhantomJS vulnerabilities that might interpret HTML content as navigation commands
- Unknown behavior in the specific PhantomJS version deployed
- Possible meta-refresh or JavaScript-based navigation in injected HTML (though this is XSS, not SSRF)

## 7. Out-of-Scope Findings

### Unused Code with Potential Future Risk

**PAGE_CONTENT_IFRAME Template:**
- **Location:** `src/constants.py` lines 126-149
- **Description:** HTML template containing `<iframe {2}>` and an input field named `url`
- **Current Status:** DEAD CODE - Never referenced in `src/app.py`
- **Potential Risk:** If future developers use this template with user-controlled iframe `src` attributes, it could enable:
  - Client-side SSRF via iframe injection
  - Clickjacking attacks
  - Information disclosure via frame embedding
- **Recommendation for Future Work:** If this template is activated, implement strict allowlisting for iframe sources and validate all URL inputs

### Related Vulnerabilities (Not SSRF)

**Cross-Site Scripting (XSS):**
- **Location:** `src/app.py` line 64, rendered at line 71 of `src/constants.py`
- **Description:** User input from `solution` parameter is embedded directly into HTML attribute context without escaping
- **Impact:** Attackers can inject event handlers (e.g., `onfocus=alert(1)`) to trigger JavaScript execution in PhantomJS
- **Relationship to SSRF:** While XSS payloads can include client-side redirects or meta-refresh tags, these execute in the PhantomJS browser context, not as server-side requests. This is a different vulnerability class.
- **Status:** Out of scope for SSRF analysis; refer to XSS Analysis Specialist deliverable

## 8. Testing Evidence

### Code Analysis Performed
- **Files Reviewed:**
  - `src/app.py` (80 lines) - Main Flask application
  - `src/constants.py` (206 lines) - HTML templates
  - `src/check.js` (48 lines) - PhantomJS validation script
  - `src/requirements.txt` - Dependency manifest
  - `docker-compose.yml` - Infrastructure configuration
  - `src/Dockerfile` - Container build definition

- **Search Patterns Used:**
  - `urllib`, `requests`, `httplib`, `http.client`, `HTTPConnection`
  - `request.args.get`, `request.form.get`
  - `redirect`, `url_for`, `Response(headers=`
  - `open(`, `urlopen`, `urlretrieve`
  - `page.open`, `proc.stdin.write`
  - Keywords: `url`, `callback`, `webhook`, `redirect`, `fetch`, `link`

### Backward Taint Analysis Conducted
- **PhantomJS URL Construction:** COMPLETE
  - Source: `os.urandom(16)` (server entropy)
  - Sink: `page.open(input)` in check.js
  - User input path: ISOLATED (only affects HTML content)

- **HTTP Client Calls:** COMPLETE
  - No HTTP client invocations found despite urllib import

- **File Operations:** COMPLETE
  - All file paths hardcoded or server-generated
  - No URL-based file access

## 9. Conclusion

The XBEN-004-24 "Dalgona Challenge" application has **ZERO SSRF vulnerabilities** exploitable via the network-accessible attack surface at `http://localhost:5000/`.

**Key Findings:**
1. ✅ No HTTP client libraries are actively used (urllib imported but unused)
2. ✅ PhantomJS integration uses entirely server-controlled URLs (hardcoded localhost + random filenames)
3. ✅ No URL parameters, redirect handlers, webhook endpoints, or external service integrations exist
4. ✅ User input is isolated to HTML content injection (XSS), not URL manipulation (SSRF)
5. ✅ All file operations use local paths; no remote file fetching

**Exploitation Queue:** Empty - No SSRF vulnerabilities to pass to exploitation phase

**Recommendations:**
- No SSRF remediation required
- Monitor for future code changes that might introduce URL-based functionality (e.g., activation of PAGE_CONTENT_IFRAME template)
- Address XSS vulnerabilities identified by the XSS Analysis Specialist instead

**Analysis Confidence:** HIGH - Comprehensive white-box analysis with backward taint tracing confirms no SSRF attack vectors exist in the current codebase.