Ssrf Server Side in Echo Go with Dynamodb

Server-side SSRF occurs when an Echo Go service accepts user-controlled input and uses it to make HTTP requests to internal or external endpoints. If the service also interacts with Amazon DynamoDB, a common pattern is to fetch or store items based on identifiers derived from those HTTP calls. An attacker can supply a malicious URL that causes the backend to probe internal AWS metadata endpoints (e.g., http://169.254.169.254/latest/meta-data/) or internal AWS service endpoints that are accessible only from the host where the application runs. Because DynamoDB operations often use AWS SDK clients configured with the instance metadata service or IAM roles, an SSRF vector can pivot to abuse those credentials.

In Echo Go, routes typically bind query or body parameters and pass them to service logic. If a parameter such as table_url is used to construct a DynamoDB request (for example, to determine which table or item to act on), and the parameter is not strictly validated, an attacker can supply a URL that redirects the HTTP client used by the SDK or a custom HTTP poller to internal endpoints. This exposes sensitive metadata, including temporary security credentials, and can lead to privilege escalation or data discovery. The DynamoDB-specific risk arises when the application uses permissive HTTP clients and passes user-controlled values into request formation without whitelisting or network segmentation.

An example scenario: an Echo Go handler accepts a item_id and a source_url, fetches data from source_url, extracts a DynamoDB key, and performs a GetItem. If source_url is attacker-controlled and the HTTP client follows redirects to internal endpoints, the SDK may inadvertently use credentials reachable only via the internal network. Because DynamoDB requires correct credential context, SSRF can inadvertently expose the application’s assumed IAM role permissions, enabling the attacker to enumerate or modify DynamoDB resources they should not access.

To mitigate SSRF when working with DynamoDB in Echo Go, validate and restrict all user-controlled inputs that influence network destinations. Do not allow arbitrary URLs to dictate AWS service endpoints. Use strict allowlists for paths and hosts, and prefer configuration-driven table names rather than dynamic resolution from external input. When you must fetch external data before a DynamoDB operation, isolate the HTTP client with a strict no-proxy, no-follow-redirects policy and run the service with least-privilege IAM credentials that cannot access sensitive endpoints.

Below are concrete code examples for safe DynamoDB operations in Echo Go. The first example shows a vulnerable pattern and the second shows a remediated version with input validation and a controlled HTTP client.

// Vulnerable: user-controlled URL used to derive DynamoDB table and key
func vulnerableHandler(c echo.Context) error {
    sourceURL := c.QueryParam("source_url")
    itemID := c.QueryParam("item_id")

    // Unsafe: following redirects to internal endpoints
    resp, err := http.Get(sourceURL)
    if err != nil {
        return c.String(http.StatusInternalServerError, err.Error())
    }
    defer resp.Body.Close()

    // Assume response contains a DynamoDB key
    var payload map[string]string
    json.NewDecoder(resp.Body).Decode(&payload)
    tableName := payload["table"]
    key := payload["key"]

    // Perform DynamoDB GetItem using the derived table and key
    cfg, _ := config.LoadDefaultConfig(context.TODO())
    client := dynamodb.NewFromConfig(cfg)
    out, err := client.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String(tableName),
        Key: map[string]types.AttributeValue{
            "id": &types.AttributeValueMemberS{Value: key},
        },
    })
    if err != nil {
        return c.String(http.StatusInternalServerError, err.Error())
    }
    return c.JSON(http.StatusOK, out)
}

// Remediated: strict allowlist and controlled HTTP client
func safeHandler(c echo.Context) error {
    itemID := c.QueryParam("item_id")
    // Validate itemID format to prevent path traversal or injection
    if !regexp.MustCompile(`^[A-Za-z0-9_-]{1,128}$`).MatchString(itemID) {
        return c.String(http.StatusBadRequest, "invalid item_id")
    }

    // Use a fixed, application-controlled table name or a limited allowlist
    allowedTables := map[string]bool{"products": true, "orders": true}
    tableName := c.QueryParam("table")
    if tableName == "" || !allowedTables[tableName] {
        return c.String(http.StatusBadRequest, "invalid table")
    }

    // Controlled HTTP fetch: no redirects, short timeout, no proxy
    cli := &http.Client{
        CheckRedirect: func(req *http.Request, via []*http.Request) error {
            return http.ErrUseLastResponse
        },
        Timeout: 5 * time.Second,
    }
    // If external data is required, fetch from a vetted endpoint
    // Example: a configuration service with strict CORS and auth
    resp, err := cli.Get("https://config.example.com/items/" + itemID)
    if err != nil {
        return c.String(http.StatusBadRequest, "external fetch failed")
    }
    defer resp.Body.Close()
    if resp.StatusCode != http.StatusOK {
        return c.String(http.StatusBadRequest, "external data unavailable")
    }

    var ext map[string]string
    json.NewDecoder(resp.Body).Decode(&ext)
    // Use vetted data to build DynamoDB key, not arbitrary URLs
    key := ext["pk"]

    cfg, _ := config.LoadDefaultConfig(context.TODO())
    client := dynamodb.NewFromConfig(cfg)
    out, err := client.GetItem(context.TODO(), &dynamodb.GetItemInput{
        TableName: aws.String(tableName),
        Key: map[string]types.AttributeValue{
            "id": &types.AttributeValueMemberS{Value: key},
        },
    })
    if err != nil {
        return c.String(http.StatusInternalServerError, err.Error())
    }
    return c.JSON(http.StatusOK, out)
}

Additional remediation steps include configuring the AWS SDK to disable IMDSv1 where possible and to use a custom HTTP client with no proxy and restricted DNS resolution. Ensure that the IAM role associated with the service has only the DynamoDB permissions required for its function, avoiding broad dynamodb:* permissions. Combine these practices with runtime security monitoring to detect anomalous requests to internal metadata endpoints.