Pii Leakage in Buffalo with Dynamodb

The combination of the Buffalo web framework and Amazon DynamoDB can inadvertently expose personally identifiable information (PII) when application logic does not enforce strict access controls or data handling practices. In a Buffalo application, HTTP handlers typically interact with DynamoDB via the AWS SDK to perform database operations. If these handlers assume request parameters are safe and directly pass user-supplied identifiers (such as a user_id from a URL or query string) into a DynamoDB query or scan, sensitive records can be retrieved beyond the intended scope.

Consider an endpoint designed to fetch a user profile. A developer might write a handler that uses a path parameter like /users/:user_id and constructs a DynamoDB GetItem input using that parameter directly. Without verifying that the authenticated actor is authorized to view that specific user_id, the request returns the full item, which may contain fields such as email, phone number, or internal identifiers—constituting PII. This pattern maps to common API security risks such as BOLA (Broken Object Level Authorization) and IDOR (Insecure Direct Object Reference), which are routinely flagged by security scans.

DynamoDB’s schema-less nature amplifies the impact. A single table might store authentication metadata alongside sensitive PII fields like email, date_of_birth, or address. If an application mistakenly queries a broader set of items (e.g., using a Scan with a filter) or uses a global secondary index without proper attribute-level checks, it can unintentionally return multiple records containing PII. Insecure deserialization of DynamoDB stream records or improper handling of paginated responses can also lead to accidental exposure when logs or error messages include raw attribute values.

Another vector arises from over-permissive IAM policies attached to the service role used by the Buffalo application. If the role allows dynamodb:Scan or broad dynamodb:GetItem permissions on the table, a compromised application component or a misconfigured endpoint can enumerate large portions of the dataset. Even when the application performs basic checks, missing validation on secondary indexes or composite keys can allow an attacker to pivot across partition keys and retrieve PII that should remain isolated.

middleBrick detects these scenarios by scanning the unauthenticated attack surface of a Buffalo application that uses DynamoDB. It examines endpoint definitions, parameter usage, and—where spec is available—OpenAPI descriptions to identify endpoints that retrieve or filter data without proper authorization context. The scanner cross-references runtime behavior with definitions to highlight findings such as missing ownership checks, excessive data exposure in responses, and patterns that align with OWASP API Top 10 API1:2023 Broken Object Level Authorization. These findings come with severity ratings and remediation guidance to help teams tighten authorization and data handling around PII.

To mitigate PII leakage when using DynamoDB with Buffalo, enforce strict authorization at the handler level, validate and scope all database queries, and avoid returning unnecessary attributes. Below are concrete code examples demonstrating a secure approach.

First, structure your DynamoDB queries to fetch only the intended item using the authenticated user’s identity, not a raw path parameter. Use the AWS SDK to build a GetItem input that includes the partition key derived from the authenticated session, and avoid passing user-controlled IDs directly.

// handlers/user_profile.go
package handlers

import (
    "context"
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/service/dynamodb"
)

func ShowUserProfile(c buffalo.Context) error {
    // Assume authentication middleware has set the current user ID in context
    actorID, ok := c.Value("current_user_id").(string)
    if !ok || actorID == "" {
        return c.Error(http.StatusUnauthorized, errors.New("unauthorized"))
    }

    // The requested ID from the route must match the authenticated user
    requestedID := c.Param("user_id")
    if requestedID != actorID {
        return c.Error(http.StatusForbidden, errors.New("access denied"))
    }

    svc := dynamodb.New(session.New())
    input := &dynamodb.GetItemInput{
        TableName: aws.String("Users"),
        Key: map[string]*dynamodb.AttributeValue{
            "user_id": {
                S: aws.String(actorID),
            },
        },
        // Limit attributes to non-PII or explicitly allowed fields where possible
        ProjectionExpression: aws.String("user_id,display_name,created_at"),
    }

    result, err := svc.GetItem(input)
    if err != nil {
        return c.Error(http.StatusInternalServerError, err)
    }
    if result.Item == nil {
        return c.Error(http.StatusNotFound, errors.New("not found"))
    }

    // Map only safe fields to the response
    resp := map[string]interface{}{
        "user_id":     *result.Item["user_id"].S,
        "display_name": *result.Item["display_name"].S,
        "created_at":   *result.Item["created_at"].S,
    }
    return c.Render(http.StatusOK, r.JSON(resp))
}

This approach ensures the handler does not trust the route parameter for access decisions and limits the data returned by the DynamoDB request. It also avoids returning PII such as email or address unless explicitly required and authorized.

Second, when querying or scanning is necessary, scope the request using the authenticated user’s context and apply filter expressions to exclude sensitive attributes. For operations that require broader searches (for example, admin functions), enforce additional authorization checks and use DynamoDB’s attribute-level permissions via IAM conditions.

// handlers/admin_list_users.go
package handlers

import (
    "context"
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/service/dynamodb"
    "github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
)

func ListUsers(c buffalo.Context) error {
    // Admin-only check should be performed before this handler
    svc := dynamodb.New(session.New())
    input := &dynamodb.ScanInput{
        TableName: aws.String("Users"),
        // Use FilterExpression to exclude PII from the response
        FilterExpression: aws.String("attribute_exists(user_id)"), // example, extend as needed
        ProjectionExpression: aws.String("user_id,display_name,status"),
    }

    var users []map[string]interface{}
    err := svc.ScanPages(input, func(page *dynamodb.ScanOutput, lastPage bool) bool {
        for _, item := range page.Items {
            var u map[string]interface{}
            // Unmarshal only selected attributes
            if err := dynamodbattribute.UnmarshalMap(item, &u); err != nil {
                continue // handle error appropriately in production
            }
            users = append(users, u)
        }
        return !lastPage
    })
    if err != nil {
        return c.Error(http.StatusInternalServerError, err)
    }
    return c.Render(http.StatusOK, r.JSON(users))
}

Finally, review IAM policies associated with the Buffalo application to ensure least privilege: allow only the required DynamoDB actions on specific resources and consider conditions that restrict access by VPC or requester context. Regularly audit endpoint definitions and scan results using tools like middleBrick to identify accidental PII exposure, insecure direct object references, and gaps in authorization logic.