For years, security researchers have warned that every device left exposed online without being protected by a firewall is an attack surface.
Hackers can deploy exploits to forcibly take control over the device, or they can just connect to the exposed port if no authentication is required.
Devices hacked this way are often enslaved in malware botnets, or they serve as initial footholds and backdoors into larger corporate networks (Russian hackers already use this technique).
However, despite this being common knowledge among cyber-security and IT experts, we still have a large number of devices that are left exposed online unsecured.
In a report published earlier this month, security researchers from the Shadowserver Foundation, a non-profit organization focused on improving cyber-security practices across the world, have published a warning about companies that are leaving printers exposed online.
More specifically, Shadowserver experts scanned all the four billion routable IPv4 addresses for printers that are exposing their IPP port.
IPP stands for "Internet Printing Protocol" and, as the name suggests, is a protocol that allows users to manage internet-connected printers and send printing jobs to printers hosted online.
The difference between IPP and the multiple other printer management protocols is that IPP is a secure protocol that supports advanced features such as access control lists, authentication, and encrypted communications.
However, this doesn't mean that device owners are making use of any of these features.
Shadowserver experts said they specifically scanned the internet for IPP-capable printers that were left exposed without being protected by a firewall and allowed attackers to query for local details via the "Get-Printer-Attributes" function.
In total, experts said they usually found an average of around 80,000 printers exposing themselves online via the IPP port on a daily basis.
The number is about an eighth of all IPP-capable printers currently connected online. A normal scan with the BinaryEdge search engine reveals a daily count of between 650,000 and 700,000 devices with their IPP port (TCP/631) reachable via the internet.
There are several major problems with leaving the IPP port fully exposed online without any additional protections, such as a firewall or authentication mechanism.
For starters, Shadowserver experts say this port can be used for intelligence gathering. This was possible because a large percentage of IPP-capable printers returned additional information about themselves, such as printer names, locations, models, firmware versions, organization names, and even WiFi network names.
Attackers can collect this information and then search through it for enterprise networks on which they'd want to focus future attacks.
Furthermore, around a quarter of the total number of IPP-capable printers (around 21,000) also exposed their make and model details. Shadowserver researchers say exposing this information "obviously makes it much easier for attackers to locate and target populations of devices vulnerable to specific vulnerabilities."
Making matters worse, tools for IPP hacking are also readily available online. Tools like PRET (Printer Exploitation Toolkit) support IPP hacking, and they've also been used in the past to hijack printers and force them to print various propaganda messages. However, the same toolkit could also be used for much worse, such as taking over vulnerable devices entirely.
The Shadowserver Foundation, says that going forward it plans to publish daily reports on IPP exposure on its website.
"We hope that the data being shared in our new open IPP device report will lead to a reduction in the number of exposed IPP-enabled printers on the Internet, as well as raise awareness of the dangers of exposing such devices to unauthenticated scanners/attackers," the organization said in a report published this month.
Companies or national CERT teams that have subscribed to the organization's security alerts will receive automatic notifications if any IPP services are exposed online within their networks and countries' IP address spaces.
However, the Shadowserver Foundation, which has gained quite a following in the infosec community for its work in fighting and sinkholing botnets, says that companies should look into securing their printers while they still haven't been exploited.
"It is unlikely that many people need to make such a printer accessible to everyone," the organization said. "These devices should be firewalled and/or have an authentication mechanism enabled."
The Shadowserver Foundation's proactive advice to dealing with internet-exposed devices is consistent with the findings of an academic study from last year, which found that DDoS takedowns are usually ineffective, and law enforcement should focus on getting systems patched in order to limit an attack vector's usefulness for an attacker.
To configure IPP access control and IPP authentication features, users are advised to check their printers' manuals. Most printers have an IPP configuration section in their administration panel from where users can enable authentication, encryption, and limit access to the device via access lists.