Auth Bypass in Fiber with Dynamodb

Auth bypass in a Fiber-based service that uses DynamoDB as its primary data store often stems from authorization logic that is not enforced at the data-access layer. In black-box scanning, middleBrick tests endpoints that accept user-supplied identifiers (such as user IDs, group IDs, or record keys) and then query DynamoDB without validating that the authenticated principal is permitted to access the targeted item. When authorization checks are applied only at the HTTP handler level or are inconsistent across similar routes, an authenticated user can manipulate identifiers to access another user’s data, resulting in a BOLA/IDOR finding mapped to the OWASP API Top 10 and SOC2 controls.

Consider a typical endpoint /users/:userID/profile in Fiber that retrieves a profile from DynamoDB. If the handler extracts userID from parameters and uses it directly in a GetItem or Query request without verifying that the authenticated subject matches that userID, the endpoint is vulnerable. A scanner like middleBrick will detect that unauthenticated or low-privilege contexts can request arbitrary userID values and receive distinct responses, indicating missing property-level authorization. This becomes especially risky when combined with DynamoDB’s permission model: even if the service identity used by Fiber has broad read capabilities, the application must enforce user-specific filters; otherwise the API effectively exposes an unauthenticated or horizontally privileged data path.

Real-world attack patterns include changing numeric or UUID path parameters, tampering with JWT-sub claims that are not cross-checked, or exploiting missing group/role checks when querying partition keys. Because DynamoDB does not enforce row-level permissions natively, all access control must be implemented in the application. middleBrick’s checks for BOLA/IDOR, Property Authorization, and Unsafe Consumption are designed to surface these gaps by correlating spec definitions (OpenAPI parameters and response schemas) with runtime behavior, highlighting endpoints where supplied identifiers are not safely bound to the authenticated identity.

To remediate auth bypass when using DynamoDB with Fiber, enforce that every data access operation includes a condition that the authenticated subject matches the item’s ownership attribute. Avoid relying on route parameters alone; instead, derive the allowed identifier from the authenticated context and use it as a key condition or filter. The following examples show a secure pattern using the AWS SDK for Go with DynamoDB, integrated into a Fiber handler.

// Assuming: user identity is available from JWT claims after auth middleware
// authenticatedUserID is derived from verified claims, not from request input
func GetUserProfile(c *fiber.Ctx) error {
    // authenticatedUserID is set by an auth middleware earlier in the chain
    userID := c.Locals("userID").(string)
    if userID == "" {
        return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "missing user identity"})
    }

    // Build the key using the authenticated subject, not user-supplied parameters
    key := map[string]types.AttributeValue{
        "PK": &types.S{Value: "USER#" + userID},
    }
    out, err := dynamoClient.GetItem(context.Background(), &dynamodb.GetItemInput{
        TableName: aws.String("AppTable"),
        Key:       key,
    })
    if err != nil {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "failed to retrieve profile"})
    }
    if out.Item == nil {
        return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "profile not found"})
    }

    var profile Profile
    if err := attributevalue.UnmarshalMap(out.Item, &profile); err != nil {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "failed to unmarshal profile"})
    }
    return c.JSON(profile)
}

This approach ensures that the item key is derived from the authenticated identity, eliminating the risk of an attacker supplying another user’s identifier. For queries that return multiple items, apply a FilterExpression that also references the authenticated subject, and use ExpressionAttributeValues to avoid injection while keeping the authorization boundary explicit.

Additionally, apply Principle of Least Privilege to the IAM role used by Fiber. Scope the DynamoDB permissions to specific table names and conditional keys that reflect the application’s ownership model. middleBrick’s scans will surface overly permissive policies and missing checks; following its remediation guidance helps align runtime behavior with least-privilege access, reducing the likelihood of BOLA/IDOR findings that map to compliance frameworks such as OWASP API Top 10 and SOC2.