Insecure Direct Object Reference in Buffalo with Bearer Tokens

Insecure Direct Object Reference (BOLA/IDOR) occurs when an API exposes internal object references (such as numeric IDs or UUIDs) without sufficient authorization checks. In the Buffalo framework, this commonly arises in routes that use path parameters to locate records and rely solely on a Bearer Token for authentication but not for ownership or access validation. For example, a route like GET /users/:user_id/profile may authenticate the request using a Bearer Token, yet fail to verify that the authenticated user is allowed to view the profile associated with :user_id. Because Buffalo does not enforce object-level permissions by default, an attacker can manipulate the ID in the URL to access other users' data if the developer has not explicitly scoped queries to the authenticated subject.

Bearer Tokens in Buffalo are typically validated before controller actions, often via a plug that decodes the token and assigns claims to the connection. However, if the plug only ensures the token is valid and does not bind the token’s subject (e.g., user ID) to the requested resource, the endpoint becomes vulnerable. Consider a token issued for user ID 100; an attacker can change the request to /users/101 and, without proper authorization checks, retrieve or modify data they should not access. The risk is compounded when endpoints return sensitive information or allow mutations without confirming that the authenticated subject has the right to operate on the target object. Common indicators include endpoints that accept user-controlled IDs directly, lack tenant or ownership filters, and do not cross-reference the token’s claims with the database query.

Buffalo’s middleware and parameter parsing flow can inadvertently support this pattern when developers rely on convenience methods like App.Params.Get to fetch IDs without additional guards. Because the framework does not automatically enforce record-level ownership, the onus is on the developer to ensure every data access is scoped to the authenticated subject. Real-world attack patterns include iterating over numeric IDs, enumerating usernames, or leveraging predictable UUIDs to harvest data. This aligns with OWASP API Top 10 A01:2023 Broken Object Level Authorization, and can be detected during a black-box scan by observing whether different Bearer Tokens can access or modify resources owned by other tokens.

In practice, a scanner using Bearer Tokens will send requests with different object IDs while keeping the token constant, checking whether unauthorized data is returned or modified. If the API responds with 200 and meaningful data across multiple object IDs, the endpoint is likely vulnerable. Conversely, a properly secured endpoint will return 403 or 404 when the token’s subject does not own the referenced object, even if the object exists. Developers must therefore treat object identifiers as untrusted input and always enforce authorization relative to the token’s claims, rather than assuming authentication alone is sufficient.

Remediation centers on ensuring that every data access is scoped to the subject derived from the Bearer Token. In Buffalo, this is typically implemented using a plug that extracts the token, validates it, and attaches the user’s ID to the connection. Subsequent handlers must then filter queries by this user ID rather than trusting URL parameters alone. Below is a concrete example of a plug that decodes a Bearer Token and sets the current user on the connection, followed by a controller action that safely retrieves a profile using scoped lookup.

// In bootstrap/helpers.go or an equivalent initialization file
type Claims struct {
	UserID int `json:"user_id"`
	jwt.RegisteredClaims
}

func RequireAuth(conn *buffalo.Connection) error {
	auth := conn.Request.Header.Get("Authorization")
	if auth == "" {
		return conn.Error(401, errors.New("authorization header required"))
	}
	tokenString := strings.TrimPrefix(auth, "Bearer ")	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
		return []byte(os.Getenv("JWT_SECRET")), nil
	})
	if err != nil || !token.Valid {
		return conn.Error(401, errors.New("invalid token"))
	}
	if claims, ok := token.Claims.(*Claims); ok {
		conn.Set("current_user_id", claims.UserID)
	} else {
		return conn.Error(401, errors.New("invalid claims"))
	}
	return nil
}

With this plug applied globally or to specific groups, the controller can safely scope queries. For example, a profile endpoint should join or filter by the authenticated user ID instead of using the raw parameter. Here is a secure action that retrieves a user profile only when the requested ID matches the token’s subject.

func (v UsersController) ShowProfile(c buffalo.Context) error {
	requestedID, err := c.Params().GetInt("user_id")
	if err != nil {
		return c.Error(400, errors.New("invalid user_id"))
	}
	userID, ok := c.Get("current_user_id").(int)
	if !ok {
		return c.Error(401, errors.New("missing user context"))
	}
	if requestedID != userID {
		return c.Error(403, errors.New("forbidden"))
	}
	var profile Profile
	if err := connection.Select("id, display_name, email").Where("user_id = ?", userID).First(&profile); err != nil {
		return c.Error(404, errors.New("not found"))
	}
	return c.Render(200, r.JSON(profile))
}

For cases where relationships are indirect (e.g., a user accessing an organization via membership), the controller should perform a join or subquery that confirms membership rather than trusting an incoming organization ID. The key is to bind the Bearer Token’s subject to every query condition, ensuring that object identifiers are validated within the context of the authenticated subject. This approach aligns with remediation guidance from scans performed by middleBrick, which highlights missing ownership checks when using Bearer Tokens and recommends scoping all data access to the token’s claims. Developers can verify the fix by running a scan with middleBrick using Bearer Tokens and confirming that endpoints return 403 for cross-user IDs instead of exposing data.

Additionally, consider using middleware to attach the full user record rather than just the ID, which can simplify authorization logic in complex handlers. Regardless of implementation details, the principle remains the same: never treat URL-supplied object references as trustworthy when Bearer Tokens are used for authentication. Combine runtime scans from middleBrick with code-level scoping to reduce the attack surface for BOLA/IDOR in Buffalo applications.