In the first article, I explored the legacy Microsoft print subsystem and how it worked. In this article, we’ll examine why Microsoft ultimately had to move away from it.
Printers are among the least scrutinized devices on corporate networks—yet they often run full operating systems, store sensitive data, and accept unauthenticated input from across the network. This combination makes them an attractive and often overlooked target for attackers.
Modern office printers are far more than simple output devices. Alongside electro-mechanical components such as motors, lasers, and paper handling systems, they include network interfaces, USB ports, multi-core processors, and onboard storage. Each device runs firmware and embedded operating systems that are just as susceptible to vulnerabilities as traditional endpoints. As a result, printers can serve as a quiet but effective entry point into enterprise environments.
Exploiting Port 9100
One of the most widely used legacy printing methods relies on TCP port 9100 (often referred to as “RAW” printing). Its strength lies in its simplicity: any data sent to the port is treated as print-ready and processed immediately.
To see this behavior in action, enter the following into your browser:
http://:9100
For example: http://printer40:9100
Your browser will attempt to connect but display no meaningful content. When you cancel the request, many printers will interpret the partial HTTP request as printable data and produce a page of output.
While this may seem harmless, it illustrates a fundamental issue: port 9100 provides no authentication, validation, or protocol-level safeguards. Any system with network access to the printer can submit arbitrary data.
In large environments, routine security scans often trigger unintended print jobs, resulting in wasted paper and user confusion. More importantly, this behavior exposes a far more serious risk—attackers can inject arbitrary print streams into devices at will. Given that printer languages such as PCL and PostScript are effectively programmable, this creates a direct and largely unprotected input channel into the device.
Exploiting Point and Print
In the first article, we discussed the convenience of Microsoft’s Point and Print architecture. This model allowed users to connect to shared printers and automatically download and install the required drivers—without needing administrative privileges.
This convenience came at a cost.
The Windows Print Spooler service, which facilitates this process, runs in the SYSTEM security context. It performs privileged operations—such as downloading driver packages and loading associated components—on behalf of the user.
This effectively turned print servers into trusted code distribution mechanisms operating with full system privileges.
If an attacker could manipulate this process, they could execute arbitrary code in the SYSTEM context—one of the most powerful privilege levels in Windows.
This risk became reality with PrintNightmare, a vulnerability that enabled remote code execution through the spooler service.
Point and Print relies on driver packages that include binaries, configuration files, and supporting components. Particularly valuable targets were DLLs referenced in INF files—such as print processors, rendering modules, and port monitors. These components are loaded directly by the spooler service, inheriting its SYSTEM-level privileges.
Although driver packages were expected to be signed, enforcement was inconsistent. Not all referenced DLLs were individually validated at load time, and attackers could exploit this by placing malicious components in locations that the spooler trusted.
To mitigate these risks, Microsoft introduced security updates in mid-2021. By default, administrator privileges are now required to install or update printer drivers via Point and Print. While administrators can configure trusted print servers to restore some of the previous convenience, doing so reintroduces elements of the original risk.
Transport Vulnerabilities
Legacy printing protocols such as port 9100 and LPR transmit data in cleartext. In environments where an attacker gains network visibility—whether through a compromised endpoint or misconfiguration—print jobs can be intercepted and read.
This is more than a theoretical concern. Print jobs frequently contain sensitive information, including financial documents, legal materials, and medical records. Unencrypted transmission of this data represents both a security risk and a potential compliance issue.
Despite widespread adoption of encryption for web and application traffic, print infrastructure has often lagged behind. The result is a significant blind spot: sensitive data is protected in transit across most systems, but not when it is sent to the printer.
Microsoft Turns to IPP/IPPS
Faced with these challenges—unauthenticated input channels, privileged driver execution paths, and unencrypted transport—Microsoft needed a more secure and modern approach to printing.
The Internet Printing Protocol (IPP), and particularly its encrypted variant IPPS, provides a foundation for addressing many of these issues. Unlike legacy approaches, IPP is a full-featured protocol that includes structured requests, defined operations, and support for secure transport.
When combined with standards such as Mopria and IPP Everywhere, IPP enables a driverless or minimally driver-dependent printing model. This reduces reliance on complex, vendor-specific driver packages and eliminates many of the risks associated with them.
In the next article, we’ll explore how Microsoft’s Modern Print architecture leverages IPP to address these longstanding challenges and what that means for enterprise environments.
Further Reading
For readers who want a deeper understanding of Windows printing architecture—both legacy and modern—consider:
Adopting Internet Printing Protocol for Windows
https://link.springer.com/book/10.1007/979-8-8688-2010-6
This book provides a comprehensive exploration of the Windows print subsystem, from driver architecture to network printing protocols, making it a valuable reference for engineers and system administrators.
Coming Next
In the next article, we’ll take a deeper look at Microsoft’s Modern Print initiative and examine how IPP fundamentally changes the printing model—improving security, simplifying deployment, and reducing operational risk.
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