Server Side Template Injection in Adonisjs with Mongodb

Server Side Template Injection (SSTI) occurs when user-controlled data is interpolated into a server-side template without proper sanitization or strict validation. In AdonisJS, which supports multiple template engines, using a dynamic template engine (such as Edge) with data sourced from or influenced by MongoDB increases the risk if untrusted input is passed into template rendering functions.

When AdonisJS renders templates using user-influenced variables — for example, injecting a MongoDB document field directly into an Edge template — an attacker may supply template syntax as input. If the template engine evaluates that input as code, arbitrary commands can be executed on the server. Consider an endpoint that fetches a user profile from MongoDB and passes it to an Edge template:

const Profile = use('App/Models/Profile')
const profile = await Profile.findBy('username', ctx.params.username)
await ctx.view.render('profile.edge', { profile })

If the profile.bio field contains malicious Edge syntax (e.g., ${(function(){return process.exit(0)}())}) and the template does not escape or strictly sandbox expressions, the server may execute unintended operations. AdonisJS does not inherently sandbox template expressions when using certain configurations, so unsanitized MongoDB fields can become an injection vector.

Additionally, if route parameters or query strings are used to select MongoDB documents and then embedded in templates without validation, attackers can probe for template injection patterns. For instance, a crafted query parameter like ?bio={{7*7}} may produce a different output if the template evaluates expressions, revealing that user input reaches the rendering layer. This confirms a potential SSTI path when MongoDB-supplied data reaches an unsafe template context.

The combination of AdonisJS dynamic template rendering and MongoDB data flow is risky when security boundaries between data and logic are blurred. Without strict input validation, output encoding, and principle-of-least-privilege template usage, SSTI can lead to remote code execution, information disclosure, or server compromise.

To mitigate SSTI when using MongoDB with AdonisJS, ensure that user input never reaches template evaluation logic and that MongoDB fields are treated as data only, not executable content.

• Use strict output escaping in Edge templates. Escape dynamic content with @escape or the double-curly syntax which auto-escapes by default:

@escape(profile.bio)

• Avoid passing raw MongoDB documents directly to templates. Instead, map documents to plain objects or DTOs that exclude functions and nested template-like structures:

const safeProfile = {
  username: profile.username,
  bio: profile.bio ? String(profile.bio) : '',
  avatar: profile.avatar
}
await ctx.view.render('profile.edge', { profile: safeProfile })

• Validate and sanitize all inputs used to query MongoDB. Use schema validation (e.g., Yup or Joi) to ensure that fields like usernames or IDs conform to expected patterns:

const profileSchema = yup.object({
  username: yup.string().matches(/^[a-zA-Z0-9_]{3,30}$/).required()
})

const validated = await profileSchema.validate(ctx.params)
const profile = await Profile.findBy('username', validated.username)

• If you must conditionally render sections based on MongoDB flags, use explicit boolean checks rather than evaluating arbitrary strings:

@if(profile.isPublic)
  <p>Public content</p>
@endif

• For applications using the MongoDB aggregation pipeline within AdonisJS, avoid assembling pipeline stages directly from user input. Use parameterized stages and whitelist allowed operators:

const allowedStages = ['match', 'project', 'sort']
if (!allowedStages.includes(userStage)) {
  throw new Error('Invalid stage')
}
const cursor = Profile.aggregate([{ $match: { status: 'active' } }])

• Keep template engines configured securely. Prefer auto-escaping mechanisms and disable any eval-like or sandbox-bypass options in your Edge compiler settings:

// In start/edge.js
const edge = require('@edgejs/core')

exports.edge = {
  compiler: {
    functions: {
      escape: (value) => String(value)
    },
    // Avoid enabling JavaScript evaluation in expressions
    evaluateExpressions: false
  }
}