Command Injection in Gin with Dynamodb

Command Injection occurs when untrusted input is concatenated into a system command executed by the application. In a Gin-based Go service that interacts with DynamoDB, this typically arises when input is used to construct shell commands for DynamoDB operations rather than using the SDK’s native, parameterized requests. For example, if a handler builds an AWS CLI string using user-controlled values and invokes it via exec.Command, an attacker can inject additional shell commands.

Consider a Gin endpoint that accepts a tableName query parameter to fetch an item via the AWS CLI. If the input is not validated and is directly interpolated into the command, an attacker can break out of the intended argument and execute arbitrary shell commands:

GET /dynamodb/get?tableName=users;cat+ /etc/passwd

In this scenario, the semicolon allows a second command to run, exposing sensitive files. Even when using the AWS SDK for Go (v2), constructing request parameters from unescaped user input can lead to unsafe behavior if the input is later used in a subprocess or in logging that is executed in a shell context. DynamoDB-specific risks include inadvertently exposing primary key values, region configurations, or IAM role assumptions through injected commands that manipulate the CLI or underlying tooling. Because DynamoDB operations often involve sensitive data, a Command Injection flaw can lead to data exfiltration or unauthorized schema exploration.

Gin does not automatically sanitize inputs bound to query or path parameters, so developers must treat all user-supplied values as untrusted. When DynamoDB interactions are performed via shell commands rather than the SDK, the attack surface expands to include shell metacharacters such as &, |, and $(). The combination of a web framework like Gin with DynamoDB thus requires strict input validation and avoidance of shell invocation to prevent Command Injection.

To prevent Command Injection when working with DynamoDB in Gin, always use the official AWS SDK for Go (v2) and avoid invoking shell commands. The SDK provides typed structures and parameterized requests that eliminate the need for string concatenation. Below are concrete, safe examples for common DynamoDB operations within a Gin handler.

Safe GetItem using AWS SDK v2

Instead of building CLI commands, use dynamodb.GetItem with a constructed key:

import (
	"context"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
	"github.com/gin-gonic/gin"
)

func GetItemHandler(c *gin.Context) {
	tableName := c.Query("tableName")
	// Validate tableName against an allowlist to prevent SSRF or unsafe resource access
	if tableName == "" || !isValidTableName(tableName) {
		c.JSON(400, gin.H{"error": "invalid table name"})
		return
	}

	keyValue := c.Query("id")
	if keyValue == "" {
		c.JSON(400, gin.H{"error": "id is required"})
		return
	}

	cfg, err := config.LoadDefaultConfig(context.TODO())
	if err != nil {
		c.JSON(500, gin.H{"error": "unable to load SDK config"})
		return
	}

	client := dynamodb.NewFromConfig(cfg)
	key := map[string]types.AttributeValue{
		"id": &types.AttributeValueMemberS{Value: keyValue},
	}

	resp, err := client.GetItem(context.TODO(), &dynamodb.GetItemInput{
		TableName: aws.String(tableName),
		Key:       key,
	})
	if err != nil {
		c.JSON(500, gin.H{"error": err.Error()})
		return
	}

	c.JSON(200, resp.Item)
}

func isValidTableName(name string) bool {
	// Allow only alphanumeric and underscore, typical DynamoDB table naming rules
	for _, r := range name {
		if !(r == '_' || r == '-' || (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9')) {
			return false
		}
	}
	return true
}

Safe Scan with Filtering
When scanning, avoid building command-like strings for filtering. Use DynamoDB’s native expression syntax:
func ScanHandler(c *gin.Context) {
	tableName := c.Query("tableName")
	if tableName == "" || !isValidTableName(tableName) {
		c.JSON(400, gin.H{"error": "invalid table name"})
		return
	}

	cfg, err := config.LoadDefaultConfig(context.TODO())
	if err != nil {
		c.JSON(500, gin.H{"error": "unable to load SDK config"})
		return
	}

	client := dynamodb.NewFromConfig(cfg)
	resp, err := client.Scan(context.TODO(), &dynamodb.ScanInput{
		TableName: aws.String(tableName),
	})
	if err != nil {
		c.JSON(500, gin.H{"error": err.Error()})
		return
	}

	c.JSON(200, resp.Items)
}

By relying on the SDK and strict input validation, you eliminate shell injection risks specific to DynamoDB operations while maintaining compatibility with Gin’s routing and middleware.