CVE-2021-34527
Published: November 3, 2021
Official Description
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 KEV Advisory
Microsoft Windows Print Spooler Remote Code Execution Vulnerability
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.
Apply updates per vendor instructions.
Risk Analysis
This vulnerability, also known as PrintNightmare, exists in the Microsoft Windows Print Spooler service and allows for remote code execution with SYSTEM privileges due to improper privileged file operations. The high EPSS score of 0.94274 and its inclusion in the KEV catalog highlight the critical urgency and high likelihood of exploitation.
This vulnerability is actively exploited in the wild and is confirmed by CISA to be part of known exploitation campaigns, indicating a severe and immediate threat. This vulnerability is remotely exploitable.
Apply all available security updates for Microsoft Windows to patch the Print Spooler service. If not required, consider disabling the Print Spooler service on critical servers.
Technical Analysis
CVE-2021-34527 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2021-34527 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Affected Vendors & Products
Exploit & PoC Resources
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-34527 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1