Secure file transfer has come a long way from the days of unencrypted FTP. And while today’s file transfer solutions like Cerberus FTP Server by Redwood provide excellent security and reliability, no protocol is perfect. So today, we’re reviewing the security risks of the most popular file transfer protocols to help you understand where to close any potential gaps in your own infrastructure. 

What file transfer protocols should never be used?

To start off, you should never use FTP or HTTP for file transfer. These protocols are not encrypted, and have been replaced by better, more secure successors (FTPS and HTTPS respectively). 

What risks exist across all file transfer protocols?

Most of today’s file transfer security risks come from two sources: configuration issues and human engineering/phishing attacks that capture credentials or keys. Exploits and vulnerabilities are more rare, but do occur.

  • Configuration Issues
    • Server configuration: Your server configuration will govern access levels, encryption requirements, transfer alerts, authentication credentials and more. You should review these settings with a fine-tooth comb, have another administrator double-check them and implement as many alerts as possible to warn you if an unexpected transfer occurs.
    • Network and firewall security: Every organization’s first line of defense often comes under attack at the file transfer server port level. Most organizations face regular brute force attacks looking for any open connection that they can use to seek out devices with loose security or default passwords to exploit. Ensuring you are conducting regular security scans and that your policies and settings are up to date is the ideal way to prevent these issues. 
    • Encryption at rest: While all modern file transfer protocols encrypt data in motion, your file transfer server may not encrypt data at rest. Doing so prevents third parties that have accessed your system from reading data they may encounter. 
  • Human engineering/phishing attacks Attacks that convince humans within your organization to supply their credentials or keys to a third party are by far the most common scenarios you will encounter. Your best protection against these issues is to set up data loss prevention and content adaptation protocol policies, along with multi-factor authentication to require an individual to go through a number of steps before furnishing their full list of credentials and flag any suspicious requests or data transfers. 
  • Exploits Exploits are difficult to predict, but you can prepare for them by having a plan in place for emergency patching, being prepared to air gap your systems and making sure you are following all security bulletins and keeping your software as updated as possible.

What are the security risks of FTPS?

FTPS uses SSL to encrypt transferred data, but its exchange process does have some vulnerabilities. These include:

  • SSL certificate configuration issues: These issues may range from the simple mistake of installing the certificate in the wrong location or using the wrong URL on the certificate, to more significant challenges like DNS record interference or server configuration errors. You may also experience challenges with certificate authority trust levels, depending on your setup. Mitigating these areas is typically straightforward, as your error logs will show the certificate failure. 
  • Port connections: FTPS requires at least two ports to operate, and the data connection port may change quite frequently during a transfer. This requirement may open your network to security challenges if your firewall and server security settings are not properly configured.
  • Weak authentication security: FTPS only requires a username and password for authentication, which puts much of the security in the hands of your users’ password strength.

What are the security risks of SFTP?

SFTP’s fully encrypted communication generally makes for a more secure environment, but vulnerabilities still exist. 

  • Key exchange: SFTP security requires securing the private key generated as part of the authentication process. If ownership of that key is compromised, which usually occurs via a phishing attack or administrator carelessness, your data will be at risk. The larger your organization, the more challenging this process of key management becomes. The best practice is to regularly rotate keys to minimize the potential for key theft. 
  • SSH vulnerabilities: much of the SSH architecture used across the internet relies on OpenSSH, which has been shown to have (since-patched) vulnerabilities in the past. These issues are rare, but they do occur. You can mitigate these risks by ensuring your transfer solution operates on the latest version of OpenSSH.

What are the security risks of HTTPS?

HTTPS has several risks unique to its position as the protocol of choice for web transfer:

  • Man-in-the-middle attacks: Although HTTPS encrypts data during transit, it is still susceptible to man-in-the-middle (MITM) attacks due to how traffic flows across the web. In an MITM attack, an attacker intercepts the communication between the user and the website, posing as the legitimate server. This can happen if the attacker has control over the network or if the user unknowingly connects to a malicious server. Proper certificate validation and strong encryption algorithms help mitigate this risk.
  • Web application vulnerabilities: Today’s websites are assembled with a variety of applications and components from different sources. These sources all experience the same vulnerabilities as we’ve discussed above, and if they become compromised they can serve malicious content through a channel that is already “trusted” by the client browser. 
  • Certificate issues: Similar to FTPS, HTTPS certificates can be compromised or improperly issued. They may also be revoked or spoofed to try and trick the user. 

We hope that this review has been helpful to you. If you have any concerns about security with your file transfer server, we encourage you to contact the Cerberus file transfer team