Fix Mass Assignment in Slim
Mass Assignment in Slim Framework occurs when an application blindly accepts an array of input from a request and passes it directly to a database model or ORM. This allows attackers to inject unauthorized fields—like 'role', 'is_admin', or 'balance'—into the data layer, leading to privilege escalation or data corruption.
The Vulnerable Pattern
$app->post('/user/update', function ($request, $response) { $data = $request->getParsedBody(); $userId = $data['id']; $user = User::find($userId);// VULNERABLE: Directly passing the parsed body to the update method // An attacker can send {"is_admin": true} in the POST body to escalate privileges. $user->update($data); return $response->withJson(['status' => 'success']);
});
The Secure Implementation
The fix involves breaking the direct link between the HTTP request and the persistence layer. Never trust `$request->getParsedBody()` as a source of truth for database schemas. Use property whitelisting to filter the input array, ensuring only intended fields reach the ORM. If using Eloquent, reinforce this at the model level by defining the `$fillable` property to specify exactly which columns can be mass-assigned.
$app->post('/user/update', function ($request, $response) { $data = $request->getParsedBody(); $userId = $data['id']; $user = User::find($userId);// SECURE: Explicitly whitelist the fields that are allowed to be changed $safeData = array_intersect_key($data, array_flip(['username', 'bio', 'email'])); // Alternative: Manually map fields // $user->username = $data['username'] ?? $user->username; // $user->bio = $data['bio'] ?? $user->bio; $user->update($safeData); return $response->withJson(['status' => 'success']);
});
Your Slim API
might be exposed to Mass Assignment
74% of Slim apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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