Fix NoSQL Injection in SvelteKit
NoSQL injection in the SvelteKit ecosystem typically targets the MongoDB driver or Mongoose when developers blindly trust the `request` body or URL parameters. By passing an object where a string is expected, an attacker can use operators like `$ne` (not equal) or `$gt` (greater than) to bypass authentication or dump the entire database. In SvelteKit's server-side logic, this happens most often in `+server.js` or `+page.server.js` loaders and actions.
The Vulnerable Pattern
// src/routes/login/+page.server.js export const actions = { default: async ({ request, locals }) => { const data = await request.formData(); const username = data.get('username'); const password = data.get('password');// VULNERABLE: If the client sends a JSON payload instead of FormData, // or if a middleware parses the body into an object, // an attacker can pass { "password": { "$ne": "" } } const user = await locals.db.collection('users').findOne({ username, password }); if (user) { return { success: true }; } return { success: false };
} };
The Secure Implementation
The exploit works because NoSQL engines interpret objects as query operators. If an attacker sends a payload where 'password' is an object `{"$ne": null}`, the database returns the first user it finds. To mitigate this in SvelteKit: 1) Always enforce primitive types using `String()` or `Number()` on all user-supplied input. 2) Utilize the `$eq` operator in your query objects to ensure the driver treats the input as a value rather than a command. 3) For complex schemas, use a validation library like Zod to parse and strip unexpected nested objects before they reach the database layer.
// src/routes/login/+page.server.js export const actions = { default: async ({ request, locals }) => { const data = await request.formData();// SECURE: Explicitly cast to String to strip NoSQL operators const username = String(data.get('username')); const password = String(data.get('password')); // Use the $eq operator to ensure the value is treated as a literal const user = await locals.db.collection('users').findOne({ username: { $eq: username }, password: { $eq: password } }); if (user) { return { success: true }; } return { success: false };
} };
Your SvelteKit API
might be exposed to NoSQL Injection
74% of SvelteKit apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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