In early 2023, the cybersecurity world uncovered a critical vulnerability affecting the Microsoft PostScript and PCL6 Class Printer Drivers. Known officially as CVE-2023-24876, this flaw gave attackers a path to remotely execute code on targeted Windows systems using vulnerable printer drivers. If you use network printers or manage Windows environments, understanding this issue is key. Let’s break down what CVE-2023-24876 is, why it’s dangerous, and how it can be exploited — all in plain, straightforward language.

What is CVE-2023-24876?

CVE-2023-24876 is a Remote Code Execution (RCE) vulnerability related to how Microsoft’s PostScript and PCL6 Class Printer Drivers handle certain files or print jobs. A remote, unauthenticated attacker could exploit this vulnerability by uploading or sending specially crafted files to a vulnerable system. If successful, the attacker could run code with the same privileges as the printer service, potentially gaining control over the affected computer.

Official Info

- Microsoft advisory: MSRC CVE-2023-24876
- NVD entry: NIST NVD CVE-2023-24876

How Does the Exploit Work?

To exploit CVE-2023-24876, attackers take advantage of the way printer drivers process certain file formats or print requests. By crafting a malicious PostScript or PCL6 print job and sending it to a Windows machine with the vulnerable driver, attackers can trigger memory corruption in the driver process.

When the driver tries to process the malicious data, the corrupted memory structure allows the attacker’s code to run as if it were a legitimate part of the driver, often inheriting its elevated permissions.

Attacker targets a shared printer on a network with Windows PCs using the vulnerable driver.

2. Attacker sends a malicious print job — either via remote printing, or by luring a user to open a poisoned print file.

The Windows Print Spooler (spoolsv.exe) processes the file using the PostScript or PCL6 driver.

4. The driver misinterprets the manipulated data, causing a buffer overflow or similar memory corruption issue.

Code Snippet: How an Exploit May Look

While Microsoft has not released full technical details (to avoid helping attackers), researchers and hackers often share proof-of-concept samples for educational purposes.

Below is a simplified pseudo-code example showing what an attacker might do

# Pseudo-code for sending a malicious print job exploiting CVE-2023-24876

import win32print

# Path to malicious file crafted to overflow buffer in the driver
malicious_file = "bad_ps_file.ps"

# Name of printer using the vulnerable Microsoft driver
printer_name = "Microsoft Print to PDF"

# Open printer connection
printer = win32print.OpenPrinter(printer_name)

# Start a new print job
job_info = ("Exploit Job", None, "RAW", 1)
job_id = win32print.StartDocPrinter(printer, 1, job_info)
win32print.StartPagePrinter(printer)

# Send the malicious content
with open(malicious_file, "rb") as f:
    data = f.read()
    win32print.WritePrinter(printer, data)

win32print.EndPagePrinter(printer)
win32print.EndDocPrinter(printer)
win32print.ClosePrinter(printer)

Note: The core of the exploit is in bad_ps_file.ps (or .pcl for PCL6), which the attacker must craft to exploit the driver. The above just demonstrates sending a job to the printer.

Real-World Impact

- Remote Attacks: If your printer is available over the web, or your PC is on the same network as an attacker, you’re exposed.
- Local Exploitation: Even if attackers don’t have remote access, they might trick someone into installing or opening a bad print file (email, USB, phishing).
- Privilege Escalation: Since printer services often run with high permissions, a successful exploit can give attackers more control than a normal user.

Who Is at Risk?

- Any Windows device (workstations, servers) with the Microsoft PostScript or PCL6 Class Printer Driver installed and active.

Install latest security updates.

- Run Windows Update, or manually download from Microsoft’s Security Guide.

References & Further Reading

- Microsoft CVE-2023-24876 Security Update
- NIST National Vulnerability Database entry
- Printer driver attack surface - SensePost
- Windows Printing System Attacks - NCC Group

Conclusion

CVE-2023-24876 is a stark reminder that even routine devices like printers and their drivers can become weak links in your organization’s security chain. Always keep devices updated, and remember: if you don’t need it — remove it! Stay alert for unusual print activity, and educate your colleagues about file and print safety. With proactive steps, you can block attackers from using obscure vulnerabilities like this to slip into your network.

If you want to go deeper, dig into the links above — but for daily users and sysadmins, patching and vigilance are your best friends.

Timeline

Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/23/2023 16:57:00 UTC