Sql Injection in Echo Go with Dynamodb

SQL injection is commonly associated with relational databases, but injection-style flaws can also occur when constructing NoSQL queries. With DynamoDB, the risk arises when application code builds query parameters or condition expressions by concatenating user input. In an Echo Go service that directly interpolates request values into DynamoDB API calls, an attacker can manipulate query parameters to change filter logic, bypass intended access controls, or extract unexpected data from the table.

Consider an endpoint like /users/{userID} where the handler builds a DynamoDB KeyConditionExpression using raw path parameters. If the code does not validate or parameterize the input, an attacker could provide a userID such as 123 AND begins_with(sortKey, 'secret'). Depending on how the expression is composed, this may alter the semantics of the query, exposing other users' data or revealing the presence of sensitive attributes. While DynamoDB does not support traditional SQL parsing, injection-like behavior can occur via malformed or unescaped expression attribute values, especially when expressions are assembled with string formatting.

The Echo Go framework simplifies route definition but does not enforce any safe query-building patterns. If developers construct Input objects directly from c.Param() or c.FormValue() and then embed those values into DynamoDB SDK input structs, they can inadvertently create endpoints that reflect user input into API requests without validation. This becomes critical when combined with features like DynamoDB Streams or exported backups: unchecked input can lead to excessive data retrieval or noisy scans that may be leveraged for enumeration. The interplay between Echo Go's flexible routing and DynamoDB's expression syntax increases the importance of strict schema validation and explicit parameterization.

Another scenario involves secondary indexes. An attacker might supply crafted query parameters that target Global Secondary Indexes (GSIs) with unexpected partition or sort keys, causing the service to consume disproportionate read capacity or return sensitive items. Because DynamoDB access patterns are defined by the application, missing authorization checks on the query parameters can turn an unauthenticated endpoint into a data exposure vector. Therefore, treating DynamoDB as fully trusted or assuming it cannot be abused via malformed expressions is a common misstep.

Remediation centers on never directly interpolating user input into DynamoDB expressions and always using the SDK's built-in parameterization features. Define strict input structures, validate and sanitize values, and use expression attribute names and values to isolate data from control logic.

Example: Safe GetItem with explicit key construction

import (
    "github.com/labstack/echo/v4"
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/service/dynamodb"
    "github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
    "net/http"
)

type UserRequest struct {
    UserID string `json:"user_id" validate:"required,alphanum,excludes=.,-"`
}

func GetUser(c echo.Context) error {
    req := new(UserRequest)
    if err := c.Bind(req); err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid payload")
    }
    if err := validate(req); err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, err.Error())
    }

    svc := dynamodb.New(session.New())
    key := map[string]*dynamodb.AttributeValue{
        "PK": {S: aws.String("USER#" + req.UserID)},
        "SK": {S: aws.String("PROFILE")},
    }
    out, err := svc.GetItem(&dynamodb.GetItemInput{
        TableName:                 aws.String("AppTable"),
        Key:                       key,
        ConsistentRead:            aws.Bool(true),
    })
    if err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
    }
    var user User
    if err := dynamodbattribute.UnmarshalMap(out.Item, &user); err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
    }
    return c.JSON(http.StatusOK, user)
}

Example: Query with expression attribute names and values

func SearchItems(c echo.Context) error {
    category := c.QueryParam("category")
    // Strict allowlist validation
    allowed := map[string]bool{"electronics": true, "books": true, "clothing": true}
    if !allowed[category] {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid category")
    }

    svc := dynamodb.New(session.New())
    input := &dynamodb.QueryInput{
        TableName: aws.String("ItemsTable"),
        IndexName: aws.String("GSI_CategoryName"),
        KeyConditionExpression: aws.String("category = :cat"),
        ExpressionAttributeNames: map[string]string{
            "#nm": "item_name",
        },
        ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
            ":cat": {S: aws.String(category)},
        },
    }
    out, err := svc.Query(input)
    if err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
    }
    var results []map[string]interface{}
    if err := dynamodbattribute.UnmarshalListOfMaps(out.Items, &results); err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
    }
    return c.JSON(http.StatusOK, results)
}

Defensive practices for Echo Go handlers

• Use context-bound validation (e.g., go-playground/validator) on all inputs before they reach DynamoDB construction code.
• Prefer allowlists for enumerated parameters such as sort key values or index names.
• Never concatenate strings to form KeyConditionExpression or FilterExpression; always use placeholders (e.g., :var) and supply values via ExpressionAttributeValues.
• Use expression attribute names (e.g., #attr) to protect reserved keywords, and keep attribute names out of raw user input.
• Instrument your Echo middleware to log suspicious patterns (e.g., presence of SQL-like keywords in parameters) for monitoring without treating logs as remediation.

These steps ensure that even when user-controlled data reaches DynamoDB API calls, it is never directly interpolated into expressions, preventing injection-style abuses while preserving the intended query semantics.