What Happens If Malware Gets On A Bastion Host? 

What Happens If Malware Gets On A Bastion Host? 


Malware can get on any machine, but it is more alarming when it infects the bastion host, which acts as the firewall between your network and the outside world. Infecting this machine can give an attacker access to all internal systems that are connected directly or indirectly to the internet. Any data traversing through this device would be visible by anyone controlling it

It would even allow attackers to operate inside your network, while staying undetected. Malicious code may also gain access to specific routes via this device, allowing them to censor traffic or intercept data.

This article discusses what happens if malware gets on the bastion host, and what can be done to prevent it from causing any damage to your network. It will also cover methods used by attackers to compromise this device, as well as ways you can identify if a breach has occurred.

How does infected traffic bypass the firewall?

A firewall is designed to block specific packets based on their source address or port. Malware, however, often abuses open ports in order to access vulnerable services inside an organization’s network directly. For example, viruses infecting web servers may attempt connections using HTTP (TCP port 80). If successful, these compromised machines can now send malicious content directly through your firewall.

Attackers would even attempt to send traffic to closed ports that have been opened by a specific service. For instance, they may attempt connections using SSH (TCP port 22) to gain access to a vulnerable instance of SecureCRT running on the bastion host.

Impact on Network Devices:

Attackers can also abuse vulnerabilities in network devices or services. One weak spot is often the remote access protocol used by employees working from home. 

This allows attackers to install malware on machines within the organization’s internal network through normal means of communication, such as email and instant messaging. Assuming they are able to infect one machine inside your corporate network, attackers could use it as a stepping stone into other segments of your system. A bastion host acts as a gateway between trusted networks and untrusted networks—in this case, the internal network and the internet. This means that it is exposed to untrusted content by default. By infecting this machine, attackers can now access systems on trusted networks through your bastion host.

How does malware bypass antivirus on a bastion host?

Attackers can use any one of several methods to get around anti-malware scanners on the bastion host:

Malware placed inside executable files (EXE) or scripts (BAT) often escapes detection due to false alerts generated by anti-virus software . These programs may identify benign executables as malicious code because of their behavior patterns and lack of virus signatures. Attackers specifically design malware in such a way that they closely mimic normal system behaviors.

Bastion hosts typically use antivirus software with content filtering capabilities to protect against malware delivery. However, attackers can take advantage of this feature by attaching their malicious code to PDFs or ZIP files. These formats are then allowed to pass through the bastion host unencrypted by the scanner’s content filter because they are writing only file types. The files themselves might not be recognized as malware at all since scans will be limited to scanning for signatures and not behavior patterns.

Malicious scripts may also be written in a way that they do not contain any executable code, making it appear as a harmless text document during a scan . Such obfuscation techniques make the script difficult for anti-virus programs to detect. In addition, these scripts can be encoded into a harmless-looking image file using steganography .

Attackers may also try to trick an anti-virus scanner by switching the encoding of their code. For example, attackers can encode malicious shellcode in Unicode format and then decode it afterwards on compromised machines. This way, the malware is encrypted during transport but executed as plain text once it reaches its destination to avoid detection.

How to protect a bastion host against malware:

To protect a bastion host from malware, your best defense is to be proactive and to follow security best practices, the same advice we always give when it comes to defending against threats. First and foremost, you need well-maintained and properly patched applications and operating systems . 

This means that you should also run up-to-date anti-virus software on your bastion hosts. Unlike on servers in your internal network, you don’t have the luxury of being able to install application whitelisting technology because few users are using these machines. Instead, running an anti-malware product on these systems with behavior detection capabilities will automatically allow all allowed processes to run while preventing all other processes from executing code. This shields the bastion host from running any malware and restricts attackers to using only legitimate software.

This is especially important if you have untrusted users accessing your internal network from a guest wireless network. Since these users are on an untrusted network, they will be more vulnerable to web-based malware attacks. If this scenario applies to your organization, it’s a good idea to position antivirus as a service within public cloud environments as a first line of defense for catching new zero-day malware variants targeting specific vulnerabilities on your bastion hosts.

As with everything security-related , there’s no guarantee that even the best protections can completely safeguard your systems . Therefore, one of the most common ways organizations handled malicious code before was to simply disconnect affected machines from your network or block them through other means.

For example, if an attacker managed to install malware on a bastion host and began scanning for internal targets, you may want to isolate the system by blocking outbound traffic originating from this device. This way, attackers won’t be able to gain any foothold into your internal networks. However, it’s important that you don’t mistake legitimate outgoing network traffic (such as instant message clients) with malicious activity. It is always better to err on the side of caution when it comes to these types of projects .


It’s unfortunate but inevitable that attackers will try different angles at exploiting your defenses in order yet one more avenue of attack open. This isn’t specific only to the bastion hosts and is a core principle of defense in depth . Therefore, you can never completely prevent all malware from getting onto these types of servers. However , there are ways to significantly reduce the chances of attackers successfully compromising your environment by following security best practices such as patching all software regularly and running up-to-date anti-malware tools on these systems (which should be treated like public cloud environments).

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