Sandbox Escape in Echo Go with Dynamodb

A sandbox escape in the context of an Echo Go service that uses Dynamodb typically occurs when user-controlled input influences DynamoDB operations in a way that allows an attacker to break out of an intended access boundary or execution context. This often maps to Broken Object Level Authorization (BOLA/IDOR) and Improper Authorization findings in an API security scan.

Consider an endpoint that retrieves an item by an identifier provided via path or query parameters. If the identifier is used directly to form a DynamoDB key condition without validating that the requesting user is authorized for that specific item, an attacker can change the identifier to access another user’s data. For example, an API designed to fetch a user’s profile might use the path parameter user_id to query DynamoDB with a key condition like user_id = :uid. If :uid is taken directly from the request without verifying that the authenticated actor matches :uid, this is a classic BOLA scenario.

Echo Go handlers often construct DynamoDB expressions dynamically. If string concatenation or unchecked formatting is used to embed identifiers into the expression, an attacker may attempt to inject additional syntax to alter the query’s semantics. While DynamoDB itself does not support SQL-style injection, malformed input can lead to unexpected expression evaluation or error handling paths that leak information or bypass intended filters. In a black-box scan, such patterns can be flagged by the Input Validation and Authorization checks, revealing whether the endpoint correctly enforces ownership.

The LLM/AI Security checks in middleBrick do not apply here because this is a traditional API authorization issue, not an LLM-specific vector. However, the scanner’s BOLA/IDOR and Property Authorization checks will test whether object-level constraints are properly enforced across different identifiers and tenants. A secure implementation ensures that every DynamoDB request includes the correct access context, such as the authenticated user’s ID, and never relies solely on client-supplied keys for authorization.

In summary, the combination of Echo Go routing, dynamic DynamoDB expression building, and insufficient authorization checks creates a pathway for unauthorized data access. A scanner run with middleBrick can surface these weaknesses through its parallel security checks, providing prioritized findings with severity and remediation guidance without requiring authentication or altering the runtime.

Remediation focuses on strict input validation, canonicalizing identifiers, and ensuring authorization is enforced before constructing DynamoDB requests. Always treat user input as untrusted and bind parameters rather than interpolating them into expression strings.

Example: Safe DynamoDB GetItem by user-scoped identifier

Assume each user can only access their own profile stored in a DynamoDB table with partition key user_id. The handler should derive the user ID from the authentication context, not from the request path.

// Echo Go handler example (using AWS SDK for Go v2)
func GetProfileHandler(c echo.Context) error {
    // Authentication/authorization context (e.g., from JWT claims)
    subject, ok := c.Get("user_id").(string)
    if !ok || subject == "" {
        return echo.NewHTTPError(http.StatusUnauthorized, "missing user context")
    }

    // Use the authenticated subject, do not trust c.Param("user_id")
    userID := subject

    out, err := svc.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String("UserProfiles"),
        Key: map[string]types.AttributeValue{
            "user_id": &types.AttributeValueMemberS{Value: userID},
        },
    })
    if err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, "failed to fetch profile")
    }
    if out.Item == nil {
        return echo.NewHTTPError(http.StatusNotFound, "profile not found")
    }

    var profile Profile
    if err := attributevalue.UnmarshalMap(out.Item, &profile); err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, "failed to decode item")
    }
    return c.JSON(http.StatusOK, profile)
}

Key points:

• The authenticated subject is sourced from the request context (e.g., after JWT verification), not from c.Param.
• The DynamoDB key is built using a bound parameter, eliminating any possibility of expression manipulation or path traversal affecting the query.
• Error handling does not expose raw DynamoDB error messages that could aid an attacker.

Example: Authorized query with partition and sort keys

If the table uses a composite key, ensure the sort key is also constrained by ownership.

// Query with enforced ownership
func ListUserItems(c echo.Context) error {
    subject, ok := c.Get("user_id").(string)
    if !ok || subject == "" {
        return echo.NewHTTPError(http.StatusUnauthorized, "missing user context")
    }

    out, err := svc.Query(context.TODO(), &dynamodb.QueryInput{
        TableName: aws.String("UserItems"),
        KeyConditionExpression: aws.String("user_id = :uid"),
        ExpressionAttributeValues: map[string]types.AttributeValue{
            ":uid": &types.AttributeValueMemberS{Value: subject},
        },
    })
    if err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, "query failed")
    }

    var items []Item
    for _, raw := range out.Items {
        var it Item
        if err := attributevalue.UnmarshalMap(raw, &it); err != nil {
            continue // or handle appropriately
        }
        items = append(items, it)
    }
    return c.JSON(http.StatusOK, items)
}

Additional remediation practices:

• Validate and canonicalize identifiers before use (e.g., trim spaces, enforce expected formats).
• Use middleware to attach the authenticated subject to the request context early in the request lifecycle.
• Enable DynamoDB client-side encryption for sensitive fields where applicable, and enforce least-privilege IAM policies for the service role used by Echo Go.
• Run periodic scans with middleBrick to detect regressions in authorization logic and input validation.