Clear-text protocols such as ftp, telnet, or http lack encryption of transported data, as well as the capability to build an authenticated connection. It means that an attacker able to sniff traffic from the network can read, modify, or corrupt the transported content. These protocols are not secure as they expose applications to an extensive range of risks:

Even in the context of isolated networks like offline environments or segmented cloud environments, the insider threat exists. Thus, attacks involving communications being sniffed or tampered with can still happen.

For example, attackers could successfully compromise prior security layers by:

In such cases, encrypting communications would decrease the chances of attackers to successfully leak data or steal credentials from other network components. By layering various security practices (segmentation and encryption, for example), the application will follow the defense-in-depth principle.

Note that using the http protocol is being deprecated by major web browsers.

In the past, it has led to the following vulnerabilities:

Ask Yourself Whether

There is a risk if you answered yes to any of those questions.

Recommended Secure Coding Practices

It is recommended to secure all transport channels, even on local networks, as it can take a single non-secure connection to compromise an entire application or system.

Sensitive Code Example

These clients from Apache commons net libraries are based on unencrypted protocols and are not recommended:

val telnet = TelnetClient(); // Sensitive

val ftpClient = FTPClient(); // Sensitive

val smtpClient = SMTPClient(); // Sensitive

Unencrypted HTTP connections, when using okhttp library for instance, should be avoided:

val spec: ConnectionSpec = ConnectionSpec.Builder(ConnectionSpec.CLEARTEXT) // Sensitive
  .build()

Android WebView can be configured to allow a secure origin to load content from any other origin, even if that origin is insecure (mixed content):

import android.webkit.WebView

val webView: WebView = findViewById(R.id.webview)
webView.getSettings().setMixedContentMode(MIXED_CONTENT_ALWAYS_ALLOW) // Sensitive

Compliant Solution

Use instead these clients from Apache commons net and JSch/ssh library:

JSch jsch = JSch();

if(implicit) {
  // implicit mode is considered deprecated but offer the same security than explicit mode
  val ftpsClient = FTPSClient(true);
}
else {
  val ftpsClient = FTPSClient();
}

if(implicit) {
  // implicit mode is considered deprecated but offer the same security than explicit mode
  val smtpsClient = SMTPSClient(true);
}
else {
  val smtpsClient = SMTPSClient();
  smtpsClient.connect("127.0.0.1", 25);
  if (smtpsClient.execTLS()) {
    // commands
  }
}

Perform HTTP encrypted connections, with okhttp library for instance:

val spec: ConnectionSpec =ConnectionSpec.Builder(ConnectionSpec.MODERN_TLS)
  .build()

The most secure mode for Android WebView is MIXED_CONTENT_NEVER_ALLOW:

import android.webkit.WebView

val webView: WebView = findViewById(R.id.webview)
webView.getSettings().setMixedContentMode(MIXED_CONTENT_NEVER_ALLOW)

Exceptions

No issue is reported for the following cases because they are not considered sensitive:

See