Microsoft late Tuesday pushed out an emergency patch to cover the Windows ‘PrintNightmare’ security flaw.
The out-of-band update comes more than a week after the publication of proof-of-concept exploit code sent Windows network administrators scrambling to apply pre-patch mitigations.
The issue caused major headaches in security research circles because the exploit targets CVE-2021-1675, a vulnerability that was patched by Microsoft on June 8 and originally misdiagnosed as a low-risk privilege escalation issue.
Microsoft updated its bulletin on June 21 to confirm remote code execution vectors but when the Black Hat conference announced the acceptance of a presentation on the details of the vulnerability, proof-of-concept code and a full technical write-up was published showing a path to remote code execution.
[ SEE: Windows Admins Scrambling to Contain ‘PrintNightmare’ Flaw ]
When the demo exploit code appeared on the internet, Microsoft released an advisory to confirm that the so-called ‘PrintNightmare’ bug was an entirely new security flaw that exposed users to computer takeover attacks.
From Microsoft’s patch bulletin:
“A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.”
The company rated the issue as “critical” and applied a CVSS score of 8.8/8.2.
“We recommend that you install these updates immediately,” Microsoft said. “The security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527,” the company said.
The U.S. government’s CISA cybersecurity agency is encouraging Windows fleet admins to disable the Windows Print spooler service in Domain Controllers and systems that do not print.
Print Spooler, which is turned on by default on Microsoft Windows, is an executable file that’s responsible for managing all print jobs getting sent to the computer printer or print server.
Related: Microsoft Warns of Under-Attack Windows Kernel Flaw
Related: NSA Reports New Critical Microsoft Exchange Flaws
Related: Microsoft Patch Tuesday: 83 Vulnerabilities, 10 Critical, 1 Actively Exploited

Ryan Naraine is Editor-at-Large at SecurityWeek and host of the popular Security Conversations podcast series. He is a security community engagement expert who has built programs at major global brands, including Intel Corp., Bishop Fox and GReAT. Ryan is a founding-director of the Security Tinkerers non-profit, an advisor to early-stage entrepreneurs, and a regular speaker at security conferences around the world.
More from Ryan Naraine
- VMware Confirms Exploit Code Released for Critical vRealize Logging Vulnerabilities
- Gem Security Gets $11 Million Seed Investment for Cloud Incident Response Platform
- Ransomware Leads to Nantucket Public Schools Shutdown
- Sentra Raises $30 Million for DSPM Technology
- Saviynt Raises $205M; Founder Rejoins as CEO
- OpenVEX Spec Adds Clarity to Supply Chain Vulnerability Warnings
- Tenable Launches $25 Million Early-Stage Venture Fund
- VMware Plugs Critical Code Execution Flaws
Latest News
- Fraudulent “CryptoRom” Apps Slip Through Apple and Google App Store Review Process
- US Downs Chinese Balloon Off Carolina Coast
- Microsoft: Iran Unit Behind Charlie Hebdo Hack-and-Leak Op
- Feds Say Cyberattack Caused Suicide Helpline’s Outage
- Big China Spy Balloon Moving East Over US, Pentagon Says
- Former Ubiquiti Employee Who Posed as Hacker Pleads Guilty
- Cyber Insights 2023: Venture Capital
- Atlassian Warns of Critical Jira Service Management Vulnerability
