Exploited vulnerability · CISA KEV

Is CVE-2021-34527 exploited? Yes: in CISA KEV since 3 Nov 2021

Gociux · Microsoft Windows · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-34527, Microsoft Windows Print Spooler Remote Code Execution Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 124 days after it was published. It is known to be used in ransomware campaigns. It affects Microsoft Windows. If you run it, CISA's required action is: Apply updates per vendor instructions.

What it is

Microsoft Windows Print Spooler contains an unspecified vulnerability due to the Windows Print Spooler service improperly performing privileged file operations. Successful exploitation allows an attacker to perform remote code execution with SYSTEM privileges. The vulnerability is also known under the moniker of PrintNightmare.

What to do

1. Check whether you run it. Look for Windows in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
2. Apply the fix. Apply updates per vendor instructions.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 2 Jul 2021.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

Other exploited CVEs in Windows

• CVE-2026-96951: Microsoft Windows Command Injection Vulnerability (13 Oct 2026)
• CVE-2026-81963: Microsoft Windows Link Following Vulnerability (8 Sep 2026)
• CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability (8 Sep 2026)
• CVE-2008-4250: Microsoft Windows Buffer Overflow Vulnerability (20 May 2026)
• CVE-2026-32202: Microsoft Windows Protection Mechanism Failure Vulnerability (28 Apr 2026)
• CVE-2025-60710: Microsoft Windows Link Following Vulnerability (13 Apr 2026)

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Microsoft scorecard · act-now radar.