In early 2022, Microsoft patched several critical vulnerabilities in the Windows Print Spooler service—a component repeatedly making headlines since the infamous PrintNightmare saga began. One of these vulnerabilities is CVE-2022-26786, which enables local privilege escalation (LPE) by exploiting flaws in the Print Spooler process. Unlike its related CVEs (such as CVE-2022-26787 through CVE-2022-26798 and others), CVE-2022-26786 is unique in its attack path and technical specifics. This article will walk you through its background, a simple overview, proof-of-concept (PoC) code, patch status, and references for deeper research.
What is CVE-2022-26786?
CVE-2022-26786 is a privilege escalation vulnerability discovered in the Windows Print Spooler service. This means that a user with limited permissions could exploit this flaw to gain SYSTEM-level privileges—essentially, complete control over a Windows machine. Microsoft assigned it a CVSS score of 7.8 (High).
Remote exploitation: No; local access is needed.
- CVE Page: NVD CVE-2022-26786
- Microsoft advisory: MSRC Guidance
How Does It Work?
The Windows Print Spooler service (spoolsv.exe) is responsible for handling print jobs. To allow certain operations (like printer configuration), it needs elevated system privileges.
Flaw:
CVE-2022-26786 stems from improper management of file or registry permissions by Print Spooler when handling certain tasks. A local attacker can plant malicious files or manipulate registry values, causing the spooler to load and execute code with SYSTEM privileges.
> Note: This is different from remote code execution bugs like PrintNightmare; it is purely a local privilege escalation issue.
Quick Demonstration: Proof-of-Concept
Below is a simplified code snippet simulating how a local user could abuse this vulnerability. The actual details of this exploit are more intricate and may depend on specific system internals. However, the basic idea is to make Windows Print Spooler execute a DLL payload.
Disclaimer: For ethical and legal reasons, this PoC is harmless and only demonstrates the general method.
# CVE-2022-26786 Simulated PoC (Python, for educational purposes only!)
import os
# Assume user can write to Spooler-watched directory or registry hive
FAKE_DLL_PATH = "C:\\temp\\malicious.dll"
PAYLOAD_CODE = b"Malicious DLL code here"
# Write a dummy DLL (would be actual malicious code in real attack)
with open(FAKE_DLL_PATH, "wb") as f:
f.write(PAYLOAD_CODE)
print(f"[+] Fake DLL written to: {FAKE_DLL_PATH}")
print("[+] In a real attack, Spooler would be tricked to load this DLL")
# Normally, you would manipulate registry or printer settings here
# to inject FAKE_DLL_PATH into the Spooler workflow.
print("[!] This is a proof-of-concept. Do not use for illegal purposes.")
Real world exploitation would require a more complex chain—identifying a path where low privilege users can plant files or alter configurations, then triggering the Spooler to load that code.
Exploit In The Wild
There is no confirmed evidence of this being used in real attacks before Microsoft’s patch became widely deployed, but given the Print Spooler's history, a working exploit was highly likely.
How To Protect Yourself
1. Patch your devices ASAP.
This vulnerability was fixed in the June 2022 cumulative updates for Windows. Get the update via Windows Update or directly from the Microsoft Update Catalog.
2. Disable Print Spooler if not needed:
Stop-Service spooler
Set-Service spooler -StartupType Disabled
3. Restrict Printer Driver Installation to Administrators:
Group Policy:
Computer Configuration > Administrative Templates > Printers > "Only Administrators can install printer drivers"
Why Is This Different From Other Print Spooler Bugs?
CVE-2022-26786 is distinct from CVE-2022-26787, CVE-2022-26789, CVE-2022-26790, and the rest. Each CVE represents a unique code path or security flaw in how the Print Spooler handles files, registry, or process boundaries.
Microsoft Security Advisory:
CVE-2022-26786 | Windows Print Spooler Elevation of Privilege Vulnerability
NIST NVD Entry:
PrintNightmare (Background):
CERT/CC Note VU#383432
Mimikatz PrintNightmare Timeline
Final Thoughts
Print Spooler bugs keep reminding the security world how critical Windows internals can be. If you are an admin, update your systems regularly and reconsider which services truly need to run. CVE-2022-26786 is another demonstration that seemingly innocuous Windows services can open doors to attackers if left unchecked.
Have more questions about Print Spooler attacks or want to see deeper technical write-ups? Let us know below!
Timeline
Published on: 04/15/2022 19:15:00 UTC
Last modified on: 04/19/2022 15:30:00 UTC