Insecure encryption algorithm - Anonymous cipher suites

Need

Secure encryption algorithm and cipher suite selection

Context

• Usage of Go 1.15 for developing high-performance and scalable applications
• Usage of gin-gonic/gin for building web applications in Go

Description

Non compliant code

package main

import (
	"crypto/tls"
	"log"
	"net/http"

	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()

	// Set up a server with insecure cipher suites
	server := &http.Server{
		Addr:    ":8080",
		Handler: r,
		TLSConfig: &tls.Config{
			CipherSuites: []uint16{
				tls.TLS_RSA_WITH_RC4_128_SHA,
				tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA,
				tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA,
				tls.TLS_RSA_WITH_AES_128_CBC_SHA,
				tls.TLS_ECDH_ECDSA_WITH_RC4_128_SHA,
				tls.TLS_ECDH_RSA_WITH_RC4_128_SHA,
			},
			PreferServerCipherSuites: true,
		},
	}

	log.Fatal(server.ListenAndServeTLS("server.crt", "server.key"))
}

The above code snippet is a simple server written in Go using the Gin framework. The server is configured to use a set of cipher suites that are considered insecure.

In the main function, we first create a default Gin router. Then, we create an HTTP server that listens on port 8080 and uses the Gin router as the handler.

The vulnerability lies in the TLSConfig of the server. The CipherSuites field is set to a slice of cipher suite constants that are provided by the crypto/tls package. These cipher suites are considered insecure because they use encryption algorithms like RC4 and AES in CBC mode, which are known to have several vulnerabilities.

The PreferServerCipherSuites field is set to true, which means that the server will choose the cipher suite to use. Since the server only offers insecure cipher suites, it will always choose an insecure one.

The server then starts listening and serving HTTPS requests using the ListenAndServeTLS method, with the provided certificate and key files. The server will fail to start if the files cannot be found or are invalid.

In summary, the code is vulnerable because it uses insecure cipher suites for TLS connections. This can lead to various attacks, such as data eavesdropping and man-in-the-middle attacks, which can compromise the confidentiality and integrity of the data being transmitted.

Steps

• Remove the insecure cipher suites from the TLS configuration.
• Use secure cipher suites that provide strong encryption algorithms.
• Ensure that the TLS configuration is up to date with the latest recommended cipher suites.
• Enable Perfect Forward Secrecy (PFS) by using ECDHE cipher suites.
• Set the PreferServerCipherSuites flag to true to prioritize the server's cipher suites over the client's.
• Obtain a valid SSL/TLS certificate from a trusted certificate authority.
• Configure the server to use the valid SSL/TLS certificate for secure connections.

Compliant code

package main

import (
	"crypto/tls"
	"log"
	"net/http"

	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()

	// Set up a server with secure cipher suites
	server := &http.Server{
		Addr:    ":8080",
		Handler: r,
		TLSConfig: &tls.Config{
			CipherSuites: []uint16{
				tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
				tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
				tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
				tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
				tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
				tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
			},
			PreferServerCipherSuites: true,
			MinVersion:                tls.VersionTLS12,
		},
	}

	log.Fatal(server.ListenAndServeTLS("server.crt", "server.key"))
}

The original code was vulnerable because it used insecure cipher suites in the TLS configuration. This could allow an attacker to decrypt the encrypted communication between the client and the server.

The fixed code removes the insecure cipher suites and replaces them with secure ones. The secure cipher suites use strong encryption algorithms and provide Perfect Forward Secrecy (PFS). PFS ensures that even if the server's private key is compromised, past communications remain secure.

The PreferServerCipherSuites flag is set to true to prioritize the server's cipher suites over the client's. This ensures that the server uses the most secure cipher suite that both the client and server support.

The MinVersion field is set to tls.VersionTLS12 to ensure that the server only accepts connections from clients that support TLS 1.2 or higher. This prevents downgrade attacks where an attacker forces the use of a less secure version of TLS.

Finally, the server is configured to use a valid SSL/TLS certificate for secure connections. The certificate should be obtained from a trusted certificate authority and installed on the server. The ListenAndServeTLS function is called with the paths to the certificate and private key files.

References

• 092.Insecure encryption algorithm - Anonymous cipher suites