Header Injection in Echo Go with Dynamodb

Header Injection in an Echo Go service that interacts with DynamoDB occurs when untrusted input is used to construct HTTP response headers without validation or sanitization. Because Echo Go handlers often read request parameters, query strings, or JSON payloads and then set headers such as X-Account-ID or X-Trace-Token, values that originate from or are influenced by DynamoDB item attributes can become unsafe if the application trusts DynamoDB responses implicitly.

DynamoDB itself does not inject headers, but the way application code maps DynamoDB attribute values into HTTP headers creates the injection surface. For example, a handler might retrieve a user record from DynamoDB using the AWS SDK for Go (e.g., GetItem), extract a redirect_url attribute, and then pass that value directly to echo.HeaderLocation or c.Response().Header().Set(). If the stored URL contains newline characters or malformed control characters, Echo Go will write them into the header block, potentially enabling response splitting or header manipulation. This is a classic HTTP response header injection pattern facilitated by uncontrolled data from DynamoDB.

The risk is compounded when DynamoDB is used as a configuration or feature-flag store. Suppose items contain fields such as extra_headers or cache_control that the application copies into headers. An attacker who can manipulate the DynamoDB item (via compromised credentials, a misconfigured IAM policy, or a secondary vulnerability such as IDOR) can cause the application to inject arbitrary headers like Set-Cookie or Location. In the context of the 12 parallel checks run by middleBrick, this behavior would be flagged under Authentication, BOLA/IDOR, and Property Authorization, because the issue arises from insufficient validation of data used in headers and excessive trust in identity-based access to DynamoDB.

Because Echo Go does not sanitize header values, newlines (\n, \r) and spaces enable splitting the header block, allowing injection of additional headers or even a second response line. This can lead to cache poisoning, open redirects, or session fixation. middleBrick’s active tests for Header Injection include probes that submit values containing CRLF sequences and then inspect whether those sequences appear verbatim in subsequent response headers. When DynamoDB is the source of the data, the scanner checks whether the application validates, encodes, or rejects control characters before using attribute values in headers.

Remediation begins with treating all data flowing into headers as untrusted, regardless of its source. Validate and enforce strict allowlists for header-affecting fields, especially those derived from DynamoDB. In Echo Go, use structured mapping and explicit checks rather than direct passthrough. middleBrick’s findings in this scenario include precise guidance on encoding and allowlisting, helping developers understand how to break the injection chain between DynamoDB and the HTTP response.

To secure Echo Go applications that consume DynamoDB data for header construction, apply strict validation and avoid direct header passthrough. Below are concrete, safe patterns with working DynamoDB Go SDK snippets.

1. Validate and sanitize header inputs

Never use raw DynamoDB attribute values in headers. Use an allowlist approach for known-safe values, and reject or encode anything unexpected.

import (
    "net/http"
    "strings"

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

// isSafeHeaderValue allows only alphanumeric and a few safe punctuation characters.
func isSafeHeaderValue(v string) bool {
    // Allow letters, digits, hyphen, underscore, period; reject control chars and whitespace.
    for _, r := range v {
        if !(('a' <= r && r <= 'z') || ('A' <= r && r <= 'Z') || ('0' <= r && r <= '9') || r == '-' || r == '_' || r == '.') {
            return false
        }
    }
    return true
}

func GetItemHandler(c echo.Context) error {
    id := c.Param("id")
    out, err := svc.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
        TableName: aws.String("AppConfig"),
        Key: map[string]types.AttributeValue{
            "PK": &types.AttributeValueMemberS{Value: id},
        },
    })
    if err != nil {
        return echo.NewHTTPError(http.StatusInternalServerError, "failed to get item")
    }

    redirectURL, ok := out.Item["RedirectURL"].(*types.AttributeValueMemberS)
    if !ok || redirectURL == nil {
        return c.NoContent(http.StatusOK)
    }

    url := redirectURL.Value
    if !isSafeHeaderValue(url) {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid redirect URL")
    }
    c.Response().Header().Set(echo.HeaderLocation, url)
    return c.NoContent(http.StatusSeeOther)
}

2. Avoid using DynamoDB fields that may contain newlines or spaces

If you must use free-form text, sanitize newlines and carriage returns explicitly.

import "strings"

func sanitizeHeaderInput(v string) string {
    // Remove or replace control characters that could enable header injection.
    v = strings.ReplaceAll(v, "\r", "")
    v = strings.ReplaceAll(v, "\n", "")
    return strings.TrimSpace(v)
}

func BuildCacheControl(dynamoVal *types.AttributeValueMemberS) string {
    if dynamoVal == nil {
        return "no-cache"
    }
    // Example: ensure no newline or semicolon smuggling
    val := strings.ReplaceAll(dynamoVal.Value, "\n", "")
    val = strings.ReplaceAll(val, "\r", "")
    // Further restrict to known directives in a real implementation.
    return val
}

3. Use structured configuration instead of free-form values

Prefer enumerated or constrained fields in DynamoDB to reduce risk. For example, store header directives as controlled strings and map them server-side.

type CachePolicy string

const (
    CachePublic  CachePolicy = "public"
    CachePrivate CachePolicy = "private"
)

func GetCachePolicy(c echo.Context) (CachePolicy, error) {
    pk := c.Param("policy")
    out, err := svc.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
        TableName: aws.String("Policies"),
        Key: map[string]types.AttributeValue{
            "PK": &types.AttributeValueMemberS{Value: pk},
        },
    })
    if err != nil {
        return "", err
    }
    var policy CachePolicy
    switch p := out.Item["Policy"].(type) {
    case *types.AttributeValueMemberS:
        policy = CachePolicy(p.Value)
    default:
        return "", echo.NewHTTPError(http.StatusBadRequest, "invalid policy type")
    }
    if policy != CachePublic && policy != CachePrivate {
        return "", echo.NewHTTPError(http.StatusBadRequest, "unknown policy")
    }
    return policy, nil
}

4. Leverage Echo middleware for early validation

Validate header-affecting parameters before invoking DynamoDB to reduce unnecessary calls and surface errors earlier.

func ValidateHeaderInput(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        id := c.Param("id")
        if id == "" || strings.ContainsAny(id, "\r\n") {
            return echo.NewHTTPError(http.StatusBadRequest, "invalid id")
        }
        return next(c)
    }
}

By combining input validation, structured data models, and careful mapping of DynamoDB attributes to headers, you eliminate the conditions that enable Header Injection. middleBrick’s scans will highlight remaining risks such as missing validation on specific attributes and will reference checks like BOLA/IDOR and Property Authorization when DynamoDB access controls intersect with header-sensitive endpoints.