Securing Your Network from SSH Proxy Vulnerabilities

Today, most of the network equipment we interact with features IP management interfaces that allow remote access and control over the network. This is particularly prevalent in the broadcast media communication realm. The shift to IP and public cloud environments has been rapid and comprehensive, causing many devices to be exposed to third-party untrusted networks or the open internet. In cybersecurity parlance, “a larger attack surface is now potentially exposed to the public.”

Automated bots, sometimes called “SSH scanners” or “SSH brute-forcers,” actively comb the internet for unsecured or poorly secured nodes. These bots scan IP ranges, testing for open network ports and services operating on the detected devices. Upon discovering an available port, they search for vulnerabilities such as bugs, weak credentials, or configuration errors.

The primary objective of these bots is to spot SSH services, which are typically available in many pieces of equipment with subpar configurations or weak passwords, following which they attempt to gain unauthorised access to these servers.

Main concerns

Once an SSH scanner identifies a vulnerable server, it may try to establish an SSH tunnel for malicious purposes. Some potential hostile acts that could be performed through these tunnels include:

  1. Botnet recruitment: The attacker may use the compromised server as part of a botnet, allowing them to launch coordinated attacks on other systems or use the server’s resources for mining cryptocurrencies.
  2. Hide attacker & hijack bandwidth: The attacker might use the compromised server as a relay or proxy to hide their identity while carrying out other attacks, such as launching DDoS attacks or scanning for vulnerabilities on other systems. They could use the SSH tunnel to hijack your bandwidth and IP address for malicious activities.
  3. Privilege escalation: If the initial access is limited, the attacker may try to escalate privileges on the server to gain higher levels of control and access.

Picture this scenario: You have virtual servers housed on a cloud platform. Suppose an attacker (or a bot) successfully breaches these servers via SSH. In that case, they can hijack them to route enormous data traffic through your cloud provider. This results in you footing the bill for the escalated data traffic costs and masks the attacker’s activities. That’s because your devices’ IP addresses will be logged with the service providers, effectively giving the perpetrators anonymity. It’s a digital wolf in sheep’s clothing scenario that’s as cunning as it is damaging.

Detecting an SSH session hijacked for SSH tunnelling by malicious actors can be challenging because SSH is a secure and encrypted protocol. However, there are a few techniques that can be used to identify potential intrusions:

  1. Monitor for Unusual Activity: Look for multiple login attempts from the same IP address, notably failed attempts, unusual connection times, or connections from unfamiliar locations.
  2. Inspect Network Traffic: SSH tunnelling often results in a significant amount of data being transferred. If you see a single SSH connection transferring a large amount of data, that might indicate an SSH tunnel.
  3. Use Intrusion Detection Systems (IDS): An IDS can monitor network traffic and identify potential malicious activity. There are numerous IDS tools available that can provide real-time traffic analysis and packet logging.
  4. Perform Regular System Audits: Review system and security logs regularly. Look for inconsistencies, such as user account modifications or changes to system files.
  5. Check for Multiple Sessions: Look for users with multiple simultaneous sessions. While this does not necessarily indicate malicious activity, it can be a sign if it’s not typical for the user.
  6. Analyse Process Activities: Unusual processes or applications running on your system might indicate that an attacker has gained access and is running malicious software.

Easy Solution

If SSH is not needed for remote management:

1 – Disables the SSH server service on network devices. There are various ways of doing this which I can’t cover in this article. A quick Google search will provide some help.

2 – If that is not possible, block the SSH port 22 access to the network with the host’s firewall or any network firewall system.

If SSH is needed:

  • Opt for robust passwords or, better yet, use SSH keys for authentication.
  • Disable root login from remote locations and only grant access to usernames with lesser privileges on the nodes.
  • Utilise a non-standard port to lessen the chances of attack exposure.
  • Keep your system software regularly updated to remedy known vulnerabilities.
  • Limit SSH access to specific IP addresses or networks to reduce potential attack routes. Monitor SSH logs for unusual activities and set up alerts for potential security breaches.
  • If feasible, maintain the management interfaces on a private network disconnected from the internet.
  • Perform regular vulnerability assessments, and depending on the criticality of your system, consider engaging in penetration testing exercises.

Conclusion

In conclusion, SSH provides essential remote management capabilities but can also be an unwitting gateway for malicious cyber actors if not adequately secured. These unwanted intruders, automated bots or otherwise, seek out vulnerabilities, attempting to hijack SSH services for their sinister ends. The implications of SSH exploits are far-reaching, from causing financial damage by escalating data traffic costs to performing nefarious activities under the guise of your IP addresses.

However, this need not be the case. By employing robust security measures such as stronger passwords, SSH keys, turning off remote root logins, updating your system software regularly, and monitoring for unusual activity, we can make strides in protecting our network devices. We have the tools and knowledge to close this security gap and keep our digital ecosystems safer. It’s simply a matter of understanding the threat and proactively taking action to mitigate it. After all, a stitch in time saves nine, and in our increasingly digital world, those stitches are our cybersecurity measures.

Also Read

Akamai’s Proxyjacking Report
https://www.akamai.com/blog/security-research/proxyjacking-new-campaign-cybercriminal-side-hustle

Read about how SSH Bruteforce attacks work:
https://www.linuxfordevices.com/tutorials/linux/hydra-brute-force-ssh

SSH Port Forwarding
https://www.cbtnuggets.com/blog/technology/networking/what-is-ssh-port-forwarding

How to configure SSH Port Forwarding
https://medianetworksecurity.com/ssh-port-forwarding-explained/