Poodle Attack in Echo Go with Api Keys

The Poodle (Padding Oracle On Downgraded Legacy Encryption) attack targets systems that negotiate SSL 3.0 and use block ciphers in CBC mode. When an Echo Go service is configured to support or fall back to SSL 3.0, and API access is protected only by static api keys transmitted or validated in a way that leaks padding or error behavior, the combination creates a practical oracle that can be exploited.

In Echo Go, if routes are secured by checking an Authorization header containing an API key but the server still negotiates TLS with SSL 3.0 support, an attacker can perform a padding oracle attack by iteratively sending modified ciphertexts and observing differences in error messages or timing when padding validation fails. Because API keys are often handled as bearer tokens in headers, an attacker can intercept or guess a key and then use SSL 3.0 CBC padding oracles to recover bytes of encrypted traffic or session state, effectively bypassing intended secrecy provided by the key.

Echo Go’s standard HTTP server settings may inadvertently allow SSL 3.0 if the TLS configuration does not explicitly disable it. If the application validates API keys after decryption using CBC blocks and returns distinct errors for padding failures versus authentication failures, the service becomes an oracle. This is especially risky when the same endpoint echoes or processes sensitive data, as seen in patterns similar to CVE-2014-3566 where SSL 3.0 CBC padding oracles enable plaintext recovery. MiddleBrick’s SSL/TLS and Data Exposure checks highlight such misconfigurations by correlating protocol support with how errors are surfaced to the caller.

Moreover, if API keys are embedded in URLs or logged in plaintext alongside SSL 3.0 negotiated sessions, the attack surface expands. An attacker can combine a recovered session byte with a captured API key to impersonate clients or escalate abuse. Because Echo Go does not inherently disable SSL 3.0, developers must explicitly configure the TLS suite to exclude SSL 3.0 and ensure padding checks do not leak via error codes or timing, reducing the oracle feasibility.

Remediation focuses on disabling SSL 3.0, using strong cipher suites, and ensuring API key validation does not expose padding or error differentiation. Below are concrete Echo Go code examples that address the Poodle vector when API keys are in use.

// main.go
package main

import (
	"crypto/tls"
	"crypto/x509"
	"fmt"
	"net/http"
	"os"

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

func secureTLSConfig() *tls.Config {
	// Require TLS 1.2 or higher, explicitly exclude SSL 3.0 and TLS 1.0/1.1
	return &tls.Config{
		MinVersion:               tls.VersionTLS12,
		CurvePreferences:         []tls.CurveID{tls.CurveP521, tls.CurveP384, tls.CurveP256},
		PreferServerCipherSuites: true,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
		},
	}
}

func validateAPIKey(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		provided := c.Request().Header.Get("X-API-Key")
		expected := os.Getenv("EXPECTED_API_KEY")
		// Constant-time comparison to avoid timing leaks
		if !constantTimeEquals(provided, expected) {
			// Return a generic error to avoid leaking padding or auth specifics
			return c.String(http.StatusUnauthorized, "Unauthorized")
		}
		return next(c)
	}
}

// constantTimeEquals performs a constant-time byte comparison
func constantTimeEquals(a, b string) bool {
	if len(a) != len(b) {
		// Still constant-time by comparing against a dummy of same length
		b = padToLength(b, len(a))
	}
	var result byte
	for i := 0; i < len(a); i++ {
		result |= a[i] ^ b[i]
	}
	return result == 0
}

func padToLength(s string, length int) string {
	if len(s) >= length {
		return s
	}
	return s + string(make([]byte, length-len(s)))
}

func main() {
	e := echo.New()

	// Use secure TLS config on Listener (handled by Echo’s StartTLS with config)
	e.Pre(middleware.TLSWithConfig(middleware.TLSConfig{
		Config: secureTLSConfig(),
	}))

	// Middleware to enforce API key presence and constant-time validation
	e.Use(validateAPIKey)

	e.GET("/secure", func(c echo.Context) error {
		return c.String(http.StatusOK, "OK")
	})

	// Start with explicit TLS settings to ensure SSL 3.0 is not negotiated
	if err := e.StartTLS(":8443", &tls.Config{
		MinVersion: tls.VersionTLS12,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
		},
	}); err != nil {
		fmt.Fprintf(os.Stderr, "failed to start server: %v\n", err)
		os.Exit(1)
	}
}

Key remediation points: enforce TLS 1.2+, disable SSL 3.0, use AEAD cipher suites, and apply constant-time API key comparison to prevent timing or padding oracle leaks. MiddleBrick’s Authentication, Data Exposure, and Encryption checks can validate these settings in scan reports.