Crlf Injection in Echo Go with Dynamodb

Crlf Injection occurs when user-controlled data is reflected in HTTP headers without sanitization, allowing an attacker to inject newline characters (CRLF = \r\n). In an Echo Go service that uses Amazon DynamoDB as a backend, this combination can expose header injection and potentially unsafe data handling when responses are constructed from DynamoDB item attributes.

Consider an Echo Go handler that retrieves a user profile from DynamoDB and sets a custom header from a user-supplied or item attribute value. If the attribute contains a CRLF sequence, Echo will append it to the HTTP response headers, enabling injection of additional headers or response splitting. DynamoDB does not perform header-level validation; it stores and returns whatever is put into its attributes. Therefore, if an application writes user-controlled or untrusted data into a DynamoDB attribute and later uses that attribute in an HTTP header (e.g., X-User-Name, X-Request-ID), the CRLF characters are preserved and interpreted by Echo when constructing the HTTP response.

The risk is realized in a chain: an attacker submits a payload such as admin\r\nX-Injected: true into a field stored in DynamoDB. Later, when the Echo Go service reads that field and sets it as a response header, the CRLF splits the header block, causing the injected header to be processed. This can facilitate HTTP response splitting, cache poisoning, or the injection of additional malicious headers. Because the scan checks input validation and data exposure, such reflected user data in headers is flagged as a finding. The scan also cross-references the OpenAPI spec with runtime observations; if a header is defined as user-supplied in the spec but lacks validation constraints, the DynamoDB-derived value becomes an explicit injection path.

Echo Go’s routing and middleware can inadvertently propagate these values. For example, using context keys to pass DynamoDB item fields into header-setting middleware without normalization or sanitization creates a direct conduit for CRLF injection. Since the scan tests unauthenticated attack surfaces and includes input validation checks, it will highlight places where untrusted data reaches headers. The presence of DynamoDB as a persistent store does not mitigate the need for output encoding or strict allow-listing when data leaves the backend and enters the HTTP protocol.

Remediation centers on preventing CRLF characters from being reflected into HTTP headers when data originates from or is stored in DynamoDB. Apply strict validation on the server side and encode outputs appropriately. Below are concrete patterns for Echo Go with DynamoDB operations.

Safe header setting with validation

Never set headers directly from DynamoDB attributes. Validate and sanitize values before use. For example, allowlist safe characters and reject or transform CRLF characters.

import (
	"net/http"
	"strings"

	"github.com/labstack/echo/v4"
)

// validateHeader ensures no CRLF characters are present.
func validateHeader(value string) string {
	// Remove any carriage return or line feed characters.
	clean := strings.ReplaceAll(value, "\r", "")
	clean = strings.ReplaceAll(clean, "\n", "")
	// Optionally enforce allowlist: only alphanumeric, dash, underscore, space.
	// Replace anything else to prevent misuse.
	// This is a simple example; tailor regex to your use-case.
	return clean
}

func profileHandler(c echo.Context) error {
	svc := dynamodb.NewFromConfig(cfg)
	out, err := svc.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
		TableName: aws.String("UserProfiles"),
		Key: map[string]types.AttributeValue{
			"UserID": &types.AttributeValueMemberS{Value: c.Param("user_id")},
		},
	})
	if err != nil {
		return c.String(http.StatusInternalServerError, "failed to get profile")
	}
	name, ok := out.Item["DisplayName"].(*types.AttributeValueMemberS)
	if !ok || name == nil {
		return c.String(http.StatusBadRequest, "invalid profile")
	}
	safeName := validateHeader(*name.Value)
	c.Response().Header().Set("X-Display-Name", safeName)
	return c.JSON(http.StatusOK, out.Item)
}

DynamoDB put with validation on write

When storing data into DynamoDB, validate and normalize to avoid persistence of malicious patterns that could later affect other integrations.

func createProfile(c echo.Context) error {
	var req struct {
		UserID    string `json:"user_id"`
		DisplayName string `json:"display_name"`
	}
	if err := c.Bind(&req); err != nil {
		return c.String(http.StatusBadRequest, "invalid request")
	}
	safeName := validateHeader(req.DisplayName)
	_, err := svc.PutItem(c.Request().Context(), &dynamodb.PutItemInput{
		TableName: aws.String("UserProfiles"),
		Item: map[string]types.AttributeValue{
			"UserID":      &types.AttributeValueMemberS{Value: req.UserID},
			"DisplayName": &types.AttributeValueMemberS{Value: safeName},
		},
	})
	if err != nil {
		return c.String(http.StatusInternalServerError, "failed to create profile")
	}
	return c.NoContent(http.StatusCreated)
}

Middleware approach

Use an Echo middleware to normalize headers across all routes, ensuring DynamoDB-derived values are sanitized before they reach any handler. This centralizes the defense and reduces the chance of missing an endpoint.

func sanitizeHeader(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		rec := &responseRecorder{ResponseWriter: c.Response(), capture: false}
		c.Response().Writer = rec
		err := next(c)
		if err != nil {
			return err
		}
		// If you set headers from context values after DynamoDB fetch, sanitize them here.
		for k, vv := range c.Response().Header() {
			for _, v := range vv {
				clean := validateHeader(v)
				if clean != v {
					c.Response().Header().Set(k, clean)
				}
			}
		}
		return nil
	}
}

These patterns ensure that data from DynamoDB is treated as untrusted when reflected into HTTP headers. The scan’s input validation and data exposure checks align with these practices by highlighting missing validation and risky header usage. By combining server-side validation with consistent encoding, the Echo Go + DynamoDB stack avoids CRLF injection while maintaining functional integrity.