Server Side Template Injection in Django with Dynamodb

Server Side Template Injection (SSTI) occurs when an attacker can inject template code that is subsequently rendered by the server-side templating engine. In Django, this typically involves the Django template language (DTL). When user-controlled input is passed into template rendering functions—such as Template.render() or TemplateResponse—and combined with dynamic data sources like DynamoDB, the risk emerges if that input influences which data is retrieved or how it is presented.

DynamoDB itself is a NoSQL database and does not execute templates, but it can supply data that is later rendered in templates. The vulnerability chain arises when:

• An application retrieves an item from DynamoDB using user input (e.g., a record key or filter value) without strict validation.
• The retrieved data, or the user input itself, is directly interpolated into a Django template.
• The template includes dynamic template tags or filters that process user-controlled strings, enabling injection of malicious template syntax.

A concrete scenario: an endpoint accepts a user_id query parameter, fetches a profile document from DynamoDB, and renders it using Template. If the template applies user input via {{ user_bio|safe }} or uses {% include %} with a variable derived from DynamoDB, an attacker could supply a payload such as {% include "malicious_template" %} or craft input that triggers server-side code execution through template tags.

Although DynamoDB does not interpret templates, the combination increases impact because attacker-influenced data is rendered in a trusted execution context. Common indicators include use of |safe, |escape overrides, or dynamic {% include %}/{% extends %} based on database content. These patterns can lead to reflected or stored template injection, potentially exposing sensitive context or enabling server-side request forgery (SSRF) via template-driven HTTP calls if the template has access to network resources.

Real-world parallels align with OWASP API Top 10 controls around injection and improper neutralization of untrusted data. Unlike traditional SQL injection, DynamoDB’s schema-less nature may allow varied payloads that bypass simple type checks, increasing the importance of strict input validation and output encoding.

Remediation focuses on strict input validation, safe data handling, and avoiding dynamic template execution. Follow these practices when integrating DynamoDB with Django templates:

• Validate and sanitize all user input before using it in DynamoDB queries. Use Django forms or serializers with strict type and pattern checks.
• Never pass raw user input into template rendering functions. Instead, pass only transformed, validated data.
• Avoid the |safe filter on any field that may contain user-controlled content. Use |escape} where appropriate.
• Do not use dynamic template tags or includes based on database or user input. Prefer static templates and context-driven rendering.

Example of a vulnerable pattern and its fix:

# Vulnerable: user-controlled template variable used with |safe
from django import template
import boto3

register = template.Library()
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('UserProfiles')

def get_user_bio(request, user_id):
    # No validation on user_id; directly used in query and template
    response = table.get_item(Key={'user_id': user_id})
    item = response.get('Item', {})
    bio = item.get('bio', '')
    from django.template import Template, Context
    t = Template(bio)  # user-controlled template content
    return t.render(Context({}))

The above pattern allows an attacker to inject template code via the bio field stored in DynamoDB. An attacker who can control stored data could execute arbitrary template logic.

Secure alternative with explicit data handling and no dynamic template rendering:

# Secure: validated input, no dynamic template rendering
from django import template
import boto3
from django.core.exceptions import ValidationError
import re

register = template.Library()
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('UserProfiles')

def sanitize_user_id(value):
    if not re.match(r'^[a-zA-Z0-9_-]{1,64}$', value):
        raise ValidationError('Invalid user_id')
    return value

def get_user_bio(request_user_id):
    user_id = sanitize_user_id(request_user_id)
    response = table.get_item(Key={'user_id': user_id})
    item = response.get('Item', {})
    # Return plain text; no template rendering of user-controlled content
    return item.get('bio', '')

# In view
from django.shortcuts import render
def profile_view(request):
    user_id = request.GET.get('user_id', '')
    try:
        bio = get_user_bio(user_id)
    except ValidationError:
        return render(request, 'error.html', {'message': 'Invalid user identifier'})
    return render(request, 'profile.html', {'bio': bio})

Additional recommendations:

• Use DynamoDB’s condition expressions and parameterized queries to prevent injection at the database layer.
• Apply principle of least privilege to IAM roles used by boto3, limiting access to specific tables and actions.
• Enable DynamoDB Streams with caution; if used in downstream processing, validate and sanitize all stream records before any template involvement.
• Regularly audit templates for unsafe filters and dynamic includes, especially those populated from external data sources.

These steps reduce the attack surface by ensuring that data from DynamoDB is treated as untrusted until proven otherwise and that templates remain static and predictable.