Cross Site Request Forgery in Buffalo with Mongodb

Cross Site Request Forgery (CSRF) in a Buffalo application that uses MongoDB as the primary datastore occurs when an authenticated user is tricked into submitting an unintended request that the application processes against their session. Because Buffalo does not enforce automatic CSRF protection on non-GET requests by default, and because MongoDB operations rely on the application to construct commands and filter documents correctly, a missing or weak anti-CSRF mechanism can lead to unauthorized state changes in the database.

In Buffalo, typical request handling binds parameters to structs and then passes them to MongoDB update or insert operations. If an endpoint does not validate the request origin and relies only on session cookies for authentication (which are sent automatically by the browser), an attacker can craft a form on a malicious site that targets those endpoints. When the victim is authenticated, the browser includes the session cookie, and Buffalo processes the request as legitimate. Because the application may not verify intent, the corresponding MongoDB write—such as updating a user’s role, changing an email address, or creating an administrative record—can be executed without the user’s knowledge.

The exposure is compounded when the application serializes user input directly into MongoDB update operations using operators like $set without strict validation or binding. For example, an attacker could cause a state change by submitting a form with fields that map to sensitive document properties. Since Buffalo does not inherently enforce CSRF tokens on AJAX requests unless explicitly configured, any endpoint accepting JSON or form data is potentially at risk. The use of MongoDB does not introduce CSRF, but the way Buffalo routes and binds requests to database commands can inadvertently allow malicious actions to be executed under the privileges of the authenticated user.

To detect this class of issue with middleBrick, you can run a scan against your Buffalo service. The scanner includes checks for missing CSRF protections and reviews how requests interact with backend state changes, including database actions. This helps identify whether endpoints that mutate MongoDB documents are properly guarded.

Remediation focuses on ensuring that every state-modifying request is accompanied by a verifiable token or origin check, and that MongoDB operations are constrained to only the intended document fields and records.

• Use Buffalo’s built-in csrf middleware and ensure it is enabled for all non-GET routes. In buffalo.go, the middleware stack should include csrf.Protect(csrf.Secure(false)) in development and csrf.Protect(csrf.Secure(true)) in production.

package actions

import (
  "github.com/gobuffalo/buffalo"
  "github.com/gobuffalo/buffalo/middleware"
  "github.com/gobuffalo/buffalo/middleware/csrf"
)

func App() *buffalo.App {
  if app == nil {
    app = buffalo.New(buffalo.Options{
      SessionStore: &middleware.SessionCookieStore{},
    })
    app.GET("/", HomeHandler)
    app.POST("/users/update_profile", csrf.Protect(csrf.Secure(true)), UpdateProfileHandler)
    app.POST("/admin/change_role", csrf.Protect(csrf.Secure(true)), ChangeRoleHandler)
  }
  return app
}

• In handlers, validate the CSRF token explicitly when needed and bind only expected fields to your MongoDB update document. Avoid binding entire request bodies directly to update operators.

package actions

import (
  "context"
  "github.com/gobuffalo/buffalo"
  "go.mongodb.org/mongo-driver/bson"
  "go.mongodb.org/mongo-driver/mongo"
  "go.mongodb.org/mongo-driver/mongo/options"
)

type UpdateProfilePayload struct {
  Email string `json:"email" validate:"required,email"`
  Name  string `json:"name" validate:"required,min=1,max=100"`
}

func UpdateProfileHandler(c buffalo.Context) error {
  var payload UpdateProfilePayload
  if err := c.Bind(&payload); err != nil {
    return c.Render(400, r.JSON(map[string]string{"error": err.Error()}))
  }
  // Validate the CSRF token explicitly if not handled by middleware globally
  if err := csrf.Validate(c); err != nil {
    return c.Render(403, r.JSON(map[string]string{"error": "invalid csrf token"}))
  }

  // Use a controlled update document instead of binding directly to bson.M
  updateDoc := bson.D{
    {Key: "$set", Value: bson.D{
      {Key: "email", Value: payload.Email},
      {Key: "name", Value: payload.Name},
    }},
  }

  client, _ := mongo.Connect(context.Background(), options.Client().ApplyURI("mongodb://localhost:27017"))
  coll := client.Database("appdb").Collection("users")
  _, err := coll.UpdateOne(context.Background(), bson.M{"_id": c.Session().Get("user_id")}, updateDoc)
  if err != nil {
    return c.Render(500, r.JSON(map[string]string{"error": "update failed"}))
  }
  return c.Render(200, r.JSON(map[string]string{"status": "updated"}))
}

• Apply strict schema validation on the server side. Even when using dynamic MongoDB updates, validate that only allowed fields are present in the update document to prevent attackers from injecting unexpected operators or paths.

func validateAllowedUpdateFields(doc bson.D) error {
  allowed := map[string]bool{"email": true, "name": true, "preferences": true}
  for _, elem := range doc {
    if elem.Key == "$set" {
      if setDoc, ok := elem.Value.(bson.D); ok {
        for _, field := range setDoc {
          if !allowed[field.Key] {
            return fmt.Errorf("disallowed field: %s", field.Key)
          }
        }
      }
    }
  }
  return nil
}

• Ensure that session management is robust and that session identifiers are not predictable. Combine CSRF tokens with secure, HttpOnly cookies to reduce the risk of session fixation or theft that could make CSRF attacks more impactful when MongoDB operations are invoked.