JSON runs most web APIs now. If you handle data from apps, forms, or services, you meet JSON every day. In March 2024 we published "Understanding JSON: A Comprehensive Guide to Safe Data Interchange Online." The post breaks down JSON grammar, common mistakes, and clear steps to keep data exchange safe.
The article avoids jargon and gives concrete examples you can use right away. It shows why using eval on JSON is dangerous, how missing validation lets malformed data slip through, and why leaking sensitive fields in responses is a real risk. More importantly, it lists actions you should take on both client and server to reduce those risks.
Start with safe parsing. On the client, use JSON.parse instead of eval: const obj = JSON.parse(responseText); Wrap parsing in try/catch and handle errors without showing internal details. On the server, reject bad JSON early and return clear but minimal errors.
Validate with a schema. Use a JSON schema validator like Ajv to enforce types, required fields, and allowed values. Validation prevents unexpected keys and nested objects that can cause bugs or security holes. For example, require an email field to match an email pattern and reject extra fields you don’t expect.
Avoid JSONP and callback-based workarounds. JSONP injects scripts and invites cross-site injection. Prefer application/json responses and set CORS rules rather than using callbacks.
Set headers properly. Always return Content-Type: application/json. Use strict CORS: avoid * unless you truly need it. If you use credentials (cookies), set Access-Control-Allow-Credentials and whitelist origins explicitly.
Limit payload size and rate. Large JSON bodies slow clients and can hide attacks. Enforce content-length limits, paginate results, and rate-limit clients. Watch logs for sudden spikes in payload size or request rate.
Protect against prototype pollution. Don’t blindly merge untrusted objects into app state. Use safe merge utilities or create objects with Object.create(null) so attackers can’t tamper with inherited properties.
Keep secrets out of responses. Never send passwords, raw tokens, or sensitive medical data to public endpoints. If you must send identifiers, hash them or send minimal data that’s useless on its own.
Handle errors and logs carefully. Return simple error messages to users and log full details on the server for debugging. Avoid exposing stack traces or internal paths to clients.
Finally, keep libraries updated and scan dependencies. Small fixes in parsers, serializers, or middleware can close big vulnerabilities.
If you missed the March post, read it for code snippets, real-world examples, and a short checklist you can implement today. Secure JSON handling is low effort and prevents many common issues when apps exchange data online.
JSON (JavaScript Object Notation) is an essential format for data interchange on the web, derived from ECMAScript. It's vital for developers to understand its grammar, interoperability, and security implications to ensure effective and secure data exchange.