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Use of an insecure channel - SMTP

Need​

Secure communication channel for SMTP

Context​

  • Usage of Ruby for building web applications and scripting
  • Usage of net/smtp for sending emails via SMTP protocol

Description​

Non compliant code​

require 'net/smtp'

message = <<MESSAGE_END
From: Private User <[email protected]>
To: A Test User <[email protected]>
Subject: SMTP e-mail test

This is a test e-mail message.
MESSAGE_END

Net::SMTP.start('localhost') do |smtp|
  smtp.send_message message, '[email protected]', '[email protected]'
end

In the above code snippet, we are using Ruby's Net::SMTP library to send an email. The Net::SMTP.start method is used to start a SMTP session. Here, the SMTP session is started without any encryption method.

The variable message is a string that contains the email's content, including the sender, receiver, subject, and body of the email. This string is then passed to smtp.send_message method along with the sender's email and the receiver's email.

The vulnerability lies in the fact that the SMTP session is started without any security protocol. This means that the email, including its content, sender's email, and receiver's email, is sent in plain text over the network. If an attacker is able to intercept the network traffic, they can read the email's content and get the sender's and receiver's email addresses. This is a serious security issue as it can lead to information disclosure.

Steps​

  • Configure the SMTP service to use SSL/TLS encryption.
  • Update the code to use the secure version of the SMTP library.
  • Ensure that the SMTP server certificate is valid and trusted.
  • Verify that the SMTP server is configured to only accept encrypted connections.
  • Implement proper authentication mechanisms for the SMTP server.
  • Encrypt the sensitive information before sending it over the SMTP channel.

Compliant code​

require 'net/smtp'

message = <<MESSAGE_END
From: Private User <[email protected]>
To: A Test User <[email protected]>
Subject: SMTP e-mail test

This is a test e-mail message.
MESSAGE_END

Net::SMTP.start('localhost', 
                :port => 587,
                :domain => 'your.host.name',
                :user_name => 'user',
                :password => 'password',
                :authentication => :plain,
                :enable_starttls_auto => true) do |smtp|
  smtp.send_message message, '[email protected]', '[email protected]'
end

The updated code now uses the secure version of the SMTP library. The Net::SMTP.start method is now configured to use SSL/TLS encryption by setting the :enable_starttls_auto option to true. This ensures that the connection to the SMTP server is encrypted, protecting the confidentiality of the information being sent.

The :port option is set to 587, which is the standard port for secure SMTP connections. The :domain option should be set to your host name.

The :user_name and :password options are used for authentication with the SMTP server. These should be replaced with the actual username and password for your SMTP server.

The :authentication option is set to :plain, which means that the username and password are sent in plain text. However, because the connection is encrypted with SSL/TLS, this information is secure.

Before sending sensitive information over the SMTP channel, it should be encrypted. This can be done using various encryption algorithms, depending on the specific requirements of your application.

References​

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