CVE-2021-34527: in the CISA KEV catalogue
Microsoft Windows Print Spooler Remote Code Execution Vulnerability. CISA added CVE-2021-34527 to the Known Exploited Vulnerabilities catalogue on 2021-11-03 with a default due date of 2022-05-03. Known ransomware campaign use: Known. Forensic triage flag: No.
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. (CISA description)
- Vendor / product
- Microsoft Windows
- CWE
- CWE-269
- CISA required action
- Apply updates per vendor instructions.
- EPSS
- 100%, percentile 99 (scored 2026-11-03)
EPSS puts nearly every time in 100 odds (100%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2021-34527 in the CISA KEV catalogue?
Yes. CISA added CVE-2021-34527 (Microsoft Windows Print Spooler Remote Code Execution Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2021-11-03. CISA's default due date for it is 2022-05-03.
Is CVE-2021-34527 used in ransomware attacks?
CISA marks known ransomware campaign use as Known for CVE-2021-34527.
What should I do about CVE-2021-34527?
CISA's required action: Apply updates per vendor instructions.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2021-34527