Heap Overflow in Echo Go with Dynamodb

A heap-based buffer overflow in an Echo Go service that interacts with DynamoDB typically arises when unbounded or loosely validated request data is used to construct in-memory buffers or passed into low-level operations before being stored or queried in DynamoDB. While DynamoDB itself enforces strict limits on item and attribute sizes (attribute values are limited to 400 KiB), the vulnerability surface exists at the application layer where Go code marshals, unmarshals, or copies user-supplied input into fixed-size memory structures.

Consider an Echo Go handler that reads a JSON payload containing a user-controlled field used as a buffer for batch operations against DynamoDB. If the application copies this field into a fixed-length byte array or a pre-allocated slice without length checks, an oversized input can overflow the heap-allocated buffer. This can corrupt adjacent memory, potentially leading to arbitrary code execution or information disclosure. Even though DynamoDB will reject or truncate items that exceed its size limits, the overflow occurs before any DynamoDB call, during request processing and buffer preparation.

The combination increases risk when the service builds DynamoDB expressions or conditionals using unchecked input. For example, constructing an attribute value or key from concatenated user input and then sending it to DynamoDB can amplify the impact if the overflow alters control flow or metadata used in subsequent DynamoDB operations. Echo Go routes and middleware that parse form data, headers, or JSON bodies must validate lengths and types before using that data to build requests for DynamoDB.

Real-world patterns include using C-style byte arrays in Go via cgo or unsafe operations to interface with native libraries, where a large payload copied into a C buffer on the heap can overflow. More commonly in pure Go, a mis-sized byte pool or a struct with fixed-size arrays populated from user input can exhibit overflow-like behavior when assumptions about maximum sizes are violated.

Remediation focuses on strict input validation, bounded buffers, and safe data handling before any DynamoDB interaction. Use Go’s built-in length checks and avoid fixed-size buffers when working with user-controlled sizes. Prefer dynamic slices and enforce explicit limits aligned with DynamoDB’s attribute constraints.

Example: a safe Echo Go handler that prepares an item for DynamoDB PutItem with bounded input.

package main

import (
	"net/http"
	"strings"

	"github.com/labstack/echo/v4"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

const maxAttributeValueLength = 1024 // enforce a safe application-level limit well below DynamoDB’s 400 KiB

type ItemPayload struct {
	ID      string `json:"id"`
	Content string `json:"content"`
}

func CreateItem(c echo.Context) error {
	var p ItemPayload
	if err := c.Bind(&p); err != nil {
		return echo.NewHTTPError(http.StatusBadRequest, "invalid payload")
	}

	// Validate lengths before using in DynamoDB request
	if len(p.ID) == 0 || len(p.ID) > maxAttributeValueLength {
		return echo.NewHTTPError(http.StatusBadRequest, "id length invalid")
	}
	if len(p.Content) == 0 || len(p.Content) > maxAttributeValueLength {
		return echo.NewHTTPError(http.StatusBadRequest, "content length invalid")
	}

	// Build DynamoDB attribute values safely
	av := map[string]types.AttributeValue{
		"id": &types.AttributeValueMemberS{Value: p.ID},
		"content": &types.AttributeValueMemberS{Value: p.Content},
	}

	svc := dynamodb.NewFromConfig(cfg)
	_, err := svc.PutItem(c.Request().Context(), &dynamodb.PutItemInput{
		TableName: aws.String("Items"),
		Item:      av,
	})
	if err != nil {
		return echo.NewHTTPError(http.StatusInternalServerError, "failed to store item")
	}
	return c.NoContent(http.StatusCreated)
}

For batch operations or condition expressions that incorporate user input, validate and sanitize each component. Avoid building raw strings for attribute names or values using unchecked concatenation. When using the AWS SDK for Go v2, rely on strongly-typed AttributeValue structures rather than raw string injection to prevent malformed requests and ensure safe memory use.

Additionally, apply rate limiting and request size limits at the Echo Go middleware layer to reduce the likelihood of resource exhaustion before data reaches DynamoDB. The framework’s configuration allows setting maximum body sizes and timeouts that complement DynamoDB’s own limits.