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:
- sensitive data exposure
- traffic redirected to a malicious endpoint
- malware-infected software update or installer
- execution of client-side code
- corruption of critical information
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:
- bypassing isolation mechanisms
- compromising a component of the network
- getting the credentials of an internal IAM account (either from a service account or an actual person)
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
- Application data needs to be protected against falsifications or leaks when transiting over the network.
- Application data transits over an untrusted network.
- Compliance rules require the service to encrypt data in transit.
- Your application renders web pages with a relaxed mixed content policy.
- OS-level protections against clear-text traffic are deactivated.
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
- Make application data transit over a secure, authenticated and encrypted protocol like TLS or SSH. Here are a few alternatives to the most
common clear-text protocols:
- Use
ssh as an alternative to telnet.
- Use
sftp, scp, or ftps instead of ftp.
- Use
https instead of http.
- Use
SMTP over SSL/TLS or SMTP with STARTTLS instead of clear-text SMTP.
- Enable encryption of cloud components communications whenever it is possible.
- Configure your application to block mixed content when rendering web pages.
- If available, enforce OS-level deactivation of all clear-text traffic.
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:
TelnetClient telnet = new TelnetClient(); // Sensitive
FTPClient ftpClient = new FTPClient(); // Sensitive
SMTPClient smtpClient = new SMTPClient(); // Sensitive
Unencrypted HTTP connections, when using okhttp library for instance, should be avoided:
ConnectionSpec spec = new 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
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 library:
JSch jsch = new JSch();
if(implicit) {
// implicit mode is considered deprecated but offer the same security than explicit mode
FTPSClient ftpsClient = new FTPSClient(true);
}
else {
FTPSClient ftpsClient = new FTPSClient();
}
if(implicit) {
// implicit mode is considered deprecated but offer the same security than explicit mode
SMTPSClient smtpsClient = new SMTPSClient(true);
}
else {
SMTPSClient smtpsClient = new SMTPSClient();
smtpsClient.connect("127.0.0.1", 25);
if (smtpsClient.execTLS()) {
// commands
}
}
Perform HTTP encrypted connections, with okhttp library for instance:
ConnectionSpec spec = new ConnectionSpec.Builder(ConnectionSpec.MODERN_TLS)
.build();
The most secure mode for Android WebView is MIXED_CONTENT_NEVER_ALLOW:
import android.webkit.WebView
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:
- Insecure protocol scheme followed by loopback addresses like 127.0.0.1 or
localhost.
See
Documentation
Articles & blog posts
Standards
