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PrintNightmare

by Josef Weiss
July 13, 2021

PrintNightmare

On July 6, Microsoft updated its advisory to announce the availability of out-of-band patches for a critical vulnerability in its Windows Print Spooler that researchers are calling PrintNightmare.  Microsoft originally released its advisory for CVE-2021-34527 on July 1. This advisory was released in response to public reports about a proof-of-concept (PoC) exploit for CVE-2021-1675, a similar vulnerability in the Windows Print Spooler. To help clear up confusion about the vulnerability, Microsoft updated its advisory for CVE-2021-1675 to clarify that it is “similar but distinct from CVE-2021-34527.” This remote code execution (RCE) vulnerability affects all versions of Microsoft Windows.

CVE-2021-34527 is an RCE vulnerability in the Windows Print Spooler Service, which is available across desktop and server versions of Windows operating systems. The service is used to manage printers and print servers. The vulnerability exists because the service does not handle privileged file operations properly. An authenticated, remote or local attacker, could exploit this flaw in order to gain arbitrary code execution with SYSTEM privileges.

Interest is rapidly growing. Since July 1, researchers have been diligently developing PoCs for PrintNightmare. Within a week there were at least 34 public PoC exploit scripts for PrintNightmare on GitHub. These PoCs include scripts that can achieve local privilege escalation (LPE) on a targeted system, as well as remote code execution. Previous PoCs relied on the Microsoft Print System Remote Protocol (MS-RPRN) to exploit PrintNightmare.

However, on July 3, a researcher going by the nickname cube0x0, developed a PoC called SharpPrintNightmare, which uses the Microsoft Print System Asynchronous Remote Protocol (MS-PAR) instead, which confirmed that PrintNightmare could be successfully exploited against servers and desktop systems as well as domain controllers. Subsequently, Benjamin Delpy, developer of the comprehensive post-exploitation tool Mimikatz, updated the software to add support for the PrintNightmare exploit using cube0x0’s method.

Microsoft updated its advisory on July 7 to address the Point and Print aspect of this vulnerability. Specifically, they mention that while Point and Print is “not directly related to this vulnerability” its usage “weakens the local security posture” allowing for exploitation even if patches have been applied. Microsoft Security Response Center released a blog post  to announce that the cumulative patch released for CVE-2021-34527 also includes a new feature that provides users with the ability to allow non-administrative users to only install signed printer drivers which are trusted by “the installed root certificates in the system’s Trusted Root Certification Authorities”. More information on these enhanced security controls can be found in Microsoft KB5005010.

This report displays detailed information related to PrintNightmare vulnerabilities related to missing patches and vulnerable configurations. The report is used to identify systems and show progress towards mitigation. Additionally, Tenable released a Cyber Exposure Alert containing additional details and links to more information, including detailed information on critical registry key checks.  The blog can be found here.

This report is available in the Tenable.sc Feed, a comprehensive collection of dashboards, reports, Assurance Report Cards and assets. The dashboard can be easily located in the Tenable.sc Feed under the category Security Industry Trends. The dashboard requirements are:

  • SecurityCenter 5.9.0
  • Nessus 8.15.0

The Security Response Team (SRT) in Tenable Research works to dig into technical details and test proof-of-concept attacks when available, to ensure customers are fully informed of the risks. The SRT also provides breakdowns for the latest vulnerabilities on the Tenable blog. Tenable Research has released over 160,000 plugins and leads the industry on CVE coverage. Tenable's SRT team continuously works to help organizations prioritize and create remediation plans for the new threats, which often leaves very little time for reflection.

Chapters

Executive Summary: This chapter displays symmary information related to PrintNightmare vulnerabilities and the current state of Microsoft vulnerability patch managmet.  

PrintNightmare Vulnerability Details: This chapter displays all of the vulnerabilities related to the PrintNightmare vulnerability. The first section displays the counts and vulnerability details by plugin for the Windows PrintNightmare Registry Exposure (CVE-2021-34527) vulnerability. The second section displays the PrintNightmare missing patch details. 

Microsoft Patch Status: To assist organizations in understanding the current status of their Microsoft patch deployment process, this chapter brings together various elements to provide the current state of Microsoft Windows systems. This chapter is broken into three sections bringing focus to Microsoft KBs releases in 2021 and 2020, followed by a summarized section of all years prior to 2020.

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