PrintNightmare - CVE-2021-34527 Exploit Report

PrintNightmare is a critical vulnerability in the Windows Print Spooler service that allows remote code execution (RCE) and local privilege escalation (LPE). Exploited via printer driver installation APIs, this bug impacted all supported versions of Windows.

The vulnerability results from improper privilege checks when performing file operations in the Print Spooler. Remote attackers with low-privileged access can exploit it to load arbitrary DLLs as SYSTEM. It affects `RpcAddPrinterDriverEx()` functionality.

• T1068 – Exploitation for Privilege Escalation
• T1210 – Exploitation of Remote Services
• T1574.002 – Hijack Execution Flow: DLL Side-Loading
• T1543.003 – Create or Modify System Process: Windows Service

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• Apply Microsoft’s security patch released in July 2021
• Disable the Print Spooler service on servers not requiring it
• Monitor for use of `RpcAddPrinterDriverEx()` and spoolsv.exe behavior
• Use Windows Defender Exploit Guard or EDR with Print Spooler hardening

• Microsoft Advisory CVE-2021-34527
• MITRE ATT&CK Framework
• CISA Alert AA21-209A