Server Side Template Injection in Loopback with Cockroachdb

Server Side Template Injection (SSTI) in Loopback applications that interact with Cockroachdb can arise when user-controlled input is merged into server-side templates without proper validation or escaping. Loopback, a widely used Node.js framework, supports dynamic views and template rendering via engines such as Handlebars or EJS. When a developer passes request parameters directly into template variables that are later rendered by a server-side template engine, an attacker can inject template code that executes in the context of the application server.

In a Cockroachdb-backed Loopback service, this becomes particularly risky because database queries are often constructed using interpolated values. If an attacker can control a parameter that influences which template is rendered or how data is displayed, they may be able to inject logic that reads sensitive data from memory or triggers unintended behavior before a query reaches Cockroachdb. For example, a URL like /api/items?category={{special}} might feed a Handlebars template where {{special}} is not escaped, allowing an attacker to inject helpers or block expressions that execute code on the server.

The combination of Loopback’s flexible template system and Cockroachdb’s role as a backend data store can expose sensitive data or amplify the impact of an SSTI. An injected template expression could trigger additional server-side logic that issues unintended database queries or exposes internal state. Although Cockroachdb itself does not execute template code, the application layer’s misuse of user input in rendering creates a path for unauthorized information disclosure or logic manipulation. This aligns with OWASP API Top 10 categories such as Injection and Broken Object Level Authorization when template manipulation leads to unsafe data access patterns.

middleBrick scans for SSTI by testing unauthenticated endpoints that render dynamic content and by analyzing OpenAPI specs for unsafe parameter usage in template paths. For a Loopback API using Cockroachdb, a scan would flag endpoints where template variables are not properly sanitized and where database-driven responses are generated. The tool does not fix the issue but provides findings with severity ratings and remediation guidance, helping developers locate unsafe rendering logic before attackers do.

To remediate SSTI in a Loopback application communicating with Cockroachdb, ensure that all user input is strictly validated and never interpolated directly into templates or query-building logic. Use Loopback’s built-in parameter filtering and context isolation features. Prefer parameterized queries to Cockroachdb to avoid injection at the database layer, and enforce strict output encoding for any data rendered in templates.

Below is a safe pattern for querying Cockroachdb from Loopback without exposing template logic to user input:

const {CockroachdbDataSource} = require('./datasource');
const db = new CockroachdbDataSource();

async function getItemsByCategory(req, res) {
  // Assume category is extracted from validated query parameters
  const category = req.query.category;
  if (typeof category !== 'string' || !/^[a-zA-Z0-9_-]+$/.test(category)) {
    return res.status(400).json({error: 'Invalid category'});
  }
  const result = await db.execute(`
    SELECT id, name, description FROM items WHERE category = $1
  `, [category]);
  res.json(result.rows);
}

In this example, the category value is validated against a strict allowlist before being used in a parameterized SQL statement sent to Cockroachdb. This prevents both SQL injection and the possibility of malicious input reaching template rendering logic. Loopback models and datasources should be configured to use such parameterized calls consistently.

For template rendering, disable any dynamic helpers or partial resolution that could be influenced by user data. If using Handlebars, avoid eval-based helpers and ensure that any helper names are hardcoded. Here is a minimal safe configuration:

const hbs = require('express-hbs');
app.engine('hbs', hbs.express4({
  defaultLayout: 'main',
  partialsDir: __dirname + '/views/partials',
  helpers: {
    safe: function(value) {
      // Only allow known-safe transformations
      return value.replace(/&/g, '&').replace(/