This is a reconnaissance technique that is used to gather information about a computer system such as the operating system, web server, or services running on open ports. Both security professionals and attackers use this technique to identify vulnerabilities and assess the security posture of a system.
The banner is metadata displayed by services when a connection is established. They often reveal valuable details, such as software versions and configurations. While this information is designed to be helpful for system administrators, it can also be exploited by attackers who actively look for outdated and misconfigured system.
Your Role
If you are responsible for managing or maintaining IT systems, understanding how banner grabbing works is very important for securing your network. Organisations unknowingly expose information that can be easily accessed through banner grabbing. This data can provide attackers with insight into the systems and serves in use, helping them identify weaknesses to exploit.
Recognising the impact of banner grabbing increases the awareness of potential security flaws. This enables us to understand what may look like a harmless information leak, could contribute to security risks. Knowing what information is exposed, you can take proactive measures to safeguard your organisation.
Types of Banner Grabbing
Active Banner Grabbing
Active banner grabbing is the process of sending requests directly to the server and analysing the response. Typically, this involves tools that establish a direct connection to open ports or services, prompting them to display their banners. The information it provides can reveal software versions, server details, and other valuable data.
Using this method is effective but is also noisy (Attackers like to remain quite when scouting potential targets) alerting the Intrusion Detection Systems or security teams could result in the threat being blocked from direct access to the server.
Passive Banner Grabbing
Passive banner grabbing involves collecting information about a target system without directly interacting with it, leveraging the information already available on the internet or within network traffic. This process relies on the fact that some services inadvertently expose metadata that can be accessed though public repositories and cashed data. This method minimises the risk of detection, as no packets are being sent to the target, avoiding any alert triggers in the intrusion detection systems (IDS) or firewalls.
Some methods of data gathering include:
- Public repositories: such as shodan and Censys, which index devices and services exposed to the internet.
- Cashed data: from webservers, proxies, or Content Delivery Networks (CDNs).
- Network Traffic analysis: particularly within internal networks.
Risks of Banner Grabbing
The information within banners can be highly valuable to attackers. They can often reveal:
Software Versions: Identifying potentially outdated or vulnerable software that can be exploited.
Operating systems: Exposing operating system details, aid attackers to tailor their attacks.
Configuration Settings: Revealing misconfigurations that may be exploited
How You Can Defend Against Banner Grabbing
Minimise information Exposure
Its best to review your systems and see what metadata is exposed, limiting as much information as possible. For example, the web servers often display version numbers in the HTTP headers. Disabling or obscuring this information can make it much more time consuming for attackers to identify vulnerabilities.
Firewalls and Intrusion Detection Systems
Configure firewalls to restrict access to unnecessary ports and services. Deploying an IDS helps monitor network traffic and detect suspicious activity which includes looking for scans associated with active banner grabbing.
Encryption and Security Controls
It is standard practice to use HTTPS and other encryption protocols to protect data in transit, reducing the visibility of metadata, anything less is an invite from you to the internet saying, “come on in”. Implementing DNS over HTTPS (DoH) can further obscure DNS quires from wannabe attackers.
Keep The Systems Up to Date
New vulnerabilities are found all the time, its important to stay ahead of these threats. Updating systems regularly reduces the risk of black hats accessing anything from outdated versions, which can be revealed though banner information.
Monitor Public Repositories
Popular public repositories such as Shodan and Censys run scans on public facing systems and keep records of these scans. Reviewing these repositories can aid in identifying information that is made public from your network. Setting up alerts for new exposures allows you to respond quickly and minimise risk.
Final Thoughts
Banner grabbing is a mighty powerful tool that can be used for good and bad. IT professionals, it is essential to know how this works to safeguard systems and reduce the risk of exploitation and exposure. Keeping a keen eye on the information that is exposed to the public domain will aid to help create robust security controls. Ensuring systems are updated, plays a big role in keeping your organisation safe from attacks.