Server Side Template Injection on Digitalocean

Server Side Template Injection (SSTI) in Digitalocean environments typically occurs when user input is improperly handled by template engines within Digitalocean's managed services or deployed applications. Digitalocean's App Platform, Droplets running web applications, and containerized deployments are all potential targets.

The most common Digitalocean-specific manifestation involves Express.js applications deployed on Droplets or App Platform using template engines like EJS, Pug, or Handlebars. When developers use unvalidated user input directly in template rendering, attackers can inject malicious template expressions. For example:

// Vulnerable EJS template in a Digitalocean-hosted Node.js app
app.get('/profile', (req, res) => {
  const userData = {
    name: req.query.name || 'Guest',
    bio: req.query.bio || ''
  };
  res.render('profile', userData); // Attacker can inject <%- process.mainModule.require('child_process').execSync('id') %>
});

In Digitalocean's App Platform, SSTI often appears in Django applications using the default template engine. When context processors expose sensitive objects or when {% raw %} tags are misused, attackers can access Python's built-in functions:

# Vulnerable Django template in Digitalocean App Platform
{% for item in request.GET.items %}
  {{ item.0 }}: {{ item.1 }}
{% endfor %}

# Attacker injects: {{''.__class__.mro()[1].__subclasses__()[40]('/etc/passwd').read() }}

Digitalocean's Managed Databases service can be indirectly affected when SSTI leads to database credential exposure. A successful SSTI attack in an application connected to Digitalocean's PostgreSQL or MySQL databases might expose connection strings, allowing lateral movement to the database layer.

Containerized applications on Digitalocean Kubernetes or Digitalocean Container Registry are particularly vulnerable when template engines process environment variables or secrets mounted as files. An attacker injecting into a template could potentially access Kubernetes secrets or Digitalocean API credentials stored in environment variables.

Detecting SSTI in Digitalocean environments requires both automated scanning and manual testing approaches. middleBrick's API security scanner is particularly effective at identifying SSTI vulnerabilities in Digitalocean-hosted applications without requiring credentials or agents.

middleBrick's detection methodology for SSTI in Digitalocean environments includes:

• Template Expression Testing: middleBrick injects template-specific payloads like {{7*7}}, ${7*7}, and <%= 7*7 %> to identify which template engines are active and vulnerable
• Server-Side Function Access: The scanner tests for access to server-side functions by injecting payloads that attempt to execute system commands or read sensitive files
• Context-Aware Scanning: middleBrick recognizes Digitalocean-specific patterns, such as Digitalocean API keys in environment variables or Digitalocean metadata service endpoints

For manual detection in Digitalocean environments, developers should:

# Test for SSTI using curl against a Digitalocean-hosted endpoint
curl -G "https://your-app.digitalocean.app/profile" \
  --data-urlencode "name={{7*7}}" \
  --data-urlencode "bio=${7*7}"

If the response contains 49 or similar calculated values, SSTI is present. Digitalocean's App Platform logs can be monitored for suspicious template evaluation errors, which often indicate attempted SSTI attacks.

middleBrick's LLM/AI Security module specifically detects SSTI in AI-powered applications hosted on Digitalocean. When applications use template engines to generate prompts for language models, SSTI can lead to prompt injection. middleBrick tests for system prompt leakage and active prompt injection, which are critical for Digitalocean customers using AI services.

Remediating SSTI in Digitalocean environments requires both code-level fixes and platform-specific configurations. For Express.js applications on Digitalocean Droplets or App Platform:

// Secure EJS template usage in Digitalocean-hosted apps
app.get('/profile', (req, res) => {
  const userData = {
    name: sanitizeInput(req.query.name) || 'Guest',
    bio: sanitizeInput(req.query.bio) || ''
  };
  
  // Use whitelist approach for allowed properties
  const allowedProperties = ['name', 'bio'];
  const safeData = {};
  allowedProperties.forEach(prop => {
    if (userData[prop]) {
      safeData[prop] = DOMPurify.sanitize(userData[prop]);
    }
  });
  
  res.render('profile', safeData);
});

For Django applications on Digitalocean App Platform, implement template sandboxing:

# settings.py in Digitalocean Django app
TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [BASE_DIR / 'templates'],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.request',
            ],
            'libraries': {
                'custom_filters': 'myapp.templatetags.custom_filters',
            },
            'builtins': [],  # Disable dangerous builtins
        },
    },
]

Digitalocean's App Platform provides environment variable isolation that helps mitigate SSTI impact. Store sensitive data in Digitalocean's managed secrets rather than in templates:

# Digitalocean App Platform spec with secure secrets
database:
  host: ${DB_HOST}
  password: ${DB_PASSWORD}

# In your application, never expose these in templates
const dbConfig = {
  host: process.env.DB_HOST,
  password: process.env.DB_PASSWORD
};

For Digitalocean Kubernetes deployments, use security contexts to limit template engine capabilities:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: secure-app
spec:
  template:
    spec:
      securityContext:
        runAsNonRoot: true
        runAsUser: 1000
      containers:
      - name: app
        securityContext:
          allowPrivilegeEscalation: false
        env:
        - name: NODE_ENV
          value: "production"
        # Use Digitalocean secret mounts instead of env vars
        volumeMounts:
        - name: secrets
          mountPath: /app/secrets
          readOnly: true
      volumes:
      - name: secrets
        secret:
          secretName: app-secrets

middleBrick's GitHub Action can be integrated into your Digitalocean CI/CD pipeline to automatically scan for SSTI before deployment:

# .github/workflows/security.yml
name: Security Scan
on: [push, pull_request]

jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v3
    - name: Run middleBrick Scan
      uses: middlebrick/middlebrick-action@v1
      with:
        url: https://staging.your-app.digitalocean.app
        fail-on-severity: high
        token: ${{ secrets.MIDDLEBRICK_TOKEN }}