Insecure Direct Object Reference in Fiber with Dynamodb

Insecure Direct Object Reference (BOLA/IDOR) occurs when an API exposes internal object references such as database keys or IDs and allows a subject to access or modify objects without proper authorization checks. In a Go Fiber backend using Amazon DynamoDB as the persistence layer, this commonly arises when an endpoint accepts a user-supplied identifier (e.g., user_id or document_id) and uses it directly in a DynamoDB request without verifying that the requesting identity is entitled to access that specific item.

Consider a Fiber endpoint designed to retrieve a user profile stored in DynamoDB:

// Example: vulnerable endpoint in Fiber using DynamoDB
app.Get("/profiles/:user_id", func(c *fiber.Ctx) error {
    userID := c.Params("user_id")
    out, err := dynamoClient.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String("Profiles"),
        Key: map[string]types.AttributeValue{
            "user_id": &types.AttributeValueMemberS{Value: userID},
        },
    })
    if err != nil {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
    }
    if out.Item == nil {
        return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
    }
    return c.JSON(out.Item)
})

If the endpoint trusts user_id from the URL and does not compare it to the authenticated caller’s identity (e.g., from a JWT or session), an authenticated attacker can iterate over numeric or predictable IDs and read other users’ profiles. This is a classic IDOR: the object reference (the DynamoDB key) is directly controllable by the client and not validated against the requester’s permissions.

DynamoDB-specific factors can exacerbate the risk. Primary keys are often natural identifiers like usernames or numeric IDs, making them easy to guess or enumerate. If the application uses a composite key (partition and sort key), manipulating either component without authorization can lead to horizontal privilege escalation across unrelated users’ data. Moreover, DynamoDB’s low-latency responses and lack of implicit ownership checks mean there is no server-side guard that automatically prevents unauthorized reads or writes; authorization must be implemented explicitly in application logic.

Additionally, if the same endpoint supports operations like update or delete using the same user-controlled identifier, the vulnerability becomes more severe. An attacker may change their own profile fields, but if authorization is missing they might also update or delete other items by modifying the user_id parameter. This maps directly to the OWASP API Top 10 (2023) category for Broken Object Level Authorization and can be flagged by middleBrick scans under the BOLA/IDOR check, which tests whether object references are properly validated against the authenticated subject’s permissions.

In a broader security assessment, middleBrick’s parallel checks—covering Authentication, Input Validation, and Property Authorization—can surface such misconfigurations by correlating specification definitions (e.g., OpenAPI paths and parameters) with runtime behavior. For LLM-related endpoints, the scanner also examines whether outputs might inadvertently expose sensitive data, but for standard DynamoDB-driven APIs the core issue remains missing ownership validation on object references.

To remediate IDOR in Fiber when working with DynamoDB, enforce strict ownership checks and avoid direct exposure of internal keys to the client. The most reliable approach is to map authenticated subject identifiers to DynamoDB keys server-side and never allow the client to dictate the object identifier used in database operations.

Below is a secure example that retrieves a profile using the authenticated user’s subject rather than a client-supplied ID:

// Secure endpoint: use authenticated subject, not client-controlled ID
app.Get("/profiles/me", func(c *fiber.Ctx) error {
    // Assume subject is resolved from JWT or session and validated earlier
    subject, ok := c.Locals("subject").(string)
    if !ok || subject == "" {
        return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "unauthorized"})
    }
    out, err := dynamoClient.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String("Profiles"),
        Key: map[string]types.AttributeValue{
            "user_id": &types.AttributeValueMemberS{Value: subject},
        },
    })
    if err != nil {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
    }
    if out.Item == nil {
        return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
    }
    return c.JSON(out.Item)
})

If the client needs to reference resources indirectly (for example, by a client-generated alias), perform an authorization query before acting. First, fetch the item using a client-provided key, then verify that the authenticated subject owns or is allowed to access it:

// Secure pattern: resolve reference then verify ownership
app.Get("/documents/:doc_id", func(c *fiber.Ctx) error {
    docID := c.Params("doc_id")
    subject, _ := c.Locals("subject").(string)

    // Fetch document metadata using the client-supplied ID
    docOut, err := dynamoClient.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String("Documents"),
        Key: map[string]types.AttributeValue{
            "document_id": &types.AttributeValueMemberS{Value: docID},
        },
    })
    if err != nil {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
    }
    if docOut.Item == nil {\n        return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
    }

    // Authorization check: ensure the subject matches the owner stored in DynamoDB
    owner, ok := docOut.Item["owner"].(*types.AttributeValueMemberS)
    if !ok || owner.Value != subject {
        return c.Status(fiber.StatusForbidden).JSON(fiber.Map{"error": "forbidden"})
    }

    return c.JSON(docOut.Item)
})

Additional hardening steps include using least-privilege IAM roles for the DynamoDB client, enabling encryption at rest, and validating and sanitizing all inputs to avoid injection or malformed key errors. middleBrick’s scans can help verify that endpoints requiring authentication are properly gated and that object-level authorization is consistently enforced across the API surface.