Fix NoSQL Injection in Vert.x
Vert.x applications using the MongoDB client are frequently vulnerable to NoSQL injection when developers blindly trust `JsonObject` construction. By injecting operators like `$gt`, `$ne`, or `$regex` through API parameters, an attacker can bypass authentication or exfiltrate the entire database. If your input isn't strictly typed and sanitized before being passed to the driver, your data layer is wide open.
The Vulnerable Pattern
public void login(RoutingContext rc) { // Attacker sends: ?password={"$ne":"wrong"} String user = rc.request().getParam("username"); String pass = rc.request().getParam("password");JsonObject query = new JsonObject() .put("username", user) .put("password", pass); mongoClient.findOne("users", query, null, res -> { if (res.succeeded() && res.result() != null) { rc.response().setStatusCode(200).end("Authenticated"); } else { rc.response().setStatusCode(401).end(); } });
}
The Secure Implementation
The vulnerability stems from `JsonObject.put()` accepting `Object` values. When Vert.x parses a request, an attacker can supply a JSON object instead of a string. If the driver receives `{"password": {"$ne": ""}}`, the query logic is altered to 'password not equal to empty', effectively bypassing credential checks. To fix this: 1) Implement strict type checking to ensure inputs are literal strings. 2) Use the explicit `$eq` operator in your queries. This forces the MongoDB engine to treat the input as a value to match against, rather than a command to execute. 3) Sanitize input keys to strip any leading `$` characters which are reserved for MongoDB operators.
public void login(RoutingContext rc) { String user = rc.request().getParam("username"); String pass = rc.request().getParam("password");// 1. Strict Type Validation: Ensure input is a primitive string if (!(user instanceof String) || !(pass instanceof String)) { rc.response().setStatusCode(400).end("Invalid Input Type"); return; } // 2. Use explicit $eq operator to prevent operator injection JsonObject query = new JsonObject() .put("username", new JsonObject().put("$eq", user)) .put("password", new JsonObject().put("$eq", pass)); mongoClient.findOne("users", query, null, res -> { if (res.succeeded() && res.result() != null) { rc.response().setStatusCode(200).end("Authenticated"); } else { rc.response().setStatusCode(401).end(); } });
}
Your Vert.x API
might be exposed to NoSQL Injection
74% of Vert.x apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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