cbcvebase.
CVE-2021-1675
published 2021-06-08

CVE-2021-1675: Windows Print Spooler Remote Code Execution Vulnerability

PriorityP191high7.8CVSS 3.1
AVLACLPRNUIRSUCHIHAH
KEVITWEXPLOITRansomwareInitial access
CISA Known Exploited Vulnerabilitydue 2021-11-17
Exploited in the wild
EPSS
86.13%
99.7th percentile
Windows Print Spooler Remote Code Execution Vulnerability

Affected

84 ranges· showing 25
VendorProductVersion rangeFixed in
microsoftwindows_10_1507< 10.0.10240.1896710.0.10240.18967
microsoftwindows_10_1507< 10.0.10240.1896910.0.10240.18969
microsoftwindows_10_1607< 10.0.14393.446710.0.14393.4467
microsoftwindows_10_1607< 10.0.14393.447010.0.14393.4470
microsoftwindows_10_1809< 10.0.17763.199910.0.17763.1999
microsoftwindows_10_1809< 10.0.17763.202910.0.17763.2029
microsoftwindows_10_1909< 10.0.18363.162110.0.18363.1621
microsoftwindows_10_2004< 10.0.19041.105210.0.19041.1052
microsoftwindows_10_20h2< 10.0.19042.105210.0.19042.1052
microsoftwindows_10_20h2< 10.0.19042.108310.0.19042.1083
microsoftwindows_10_21h1< 10.0.19043.105210.0.19043.1052
microsoftwindows_10_21h2< 10.0.19044.141510.0.19044.1415
microsoftwindows_10_22h2< 10.0.19045.225110.0.19045.2251
microsoftwindows_10_version_1507>= 10.0.0 < 10.0.10240.1896710.0.10240.18967
microsoftwindows_10_version_1507>= 10.0.0 < 10.0.10240.1896910.0.10240.18969
microsoftwindows_10_version_1607>= 10.0.0 < 10.0.14393.446710.0.14393.4467
microsoftwindows_10_version_1607>= 10.0.0 < 10.0.14393.447010.0.14393.4470
microsoftwindows_10_version_1809>= 10.0.0 < 10.0.17763.199910.0.17763.1999
microsoftwindows_10_version_1809>= 10.0.0 < 10.0.17763.202910.0.17763.2029
microsoftwindows_10_version_1909>= 10.0.0 < 10.0.18363.162110.0.18363.1621
microsoftwindows_10_version_2004>= 10.0.0 < 10.0.19041.105210.0.19041.1052
microsoftwindows_10_version_20h2>= 10.0.0 < 10.0.19042.105210.0.19042.1052
microsoftwindows_10_version_20h2>= 10.0.0 < 10.0.19042.108310.0.19042.1083
microsoftwindows_10_version_21h1>= 10.0.0 < 10.0.19043.105210.0.19043.1052
microsoftwindows_10_version_21h2>= 10.0.0 < 10.0.19044.141510.0.19044.1415

Detection & IOCsextracted from sources · hover to see the quote

pathC:\Windows\System32\spool\drivers\x64\3\nightmare.dll
pathC:\Windows\System32\spool\drivers\x64\3\old\1\nightmare.dll
filenamenightmare.dll
path\cve-2021-1675-main-powershell\cve-2021-1675-main\cve-2021-1675.ps1
pathC:\Windows\System32\spool\drivers\x64\3\new\hello.dll
pathC:\Windows\System32\spool\drivers\x64\3\old\1\hello5.dll
commandcertutil -decode 1.txt C:\Share\hello4.dll
commandC:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe C:\Share\1.xml
snort
57876
snort
57877
yara
Exploit.Win64.CVE-2021-1675.c
  • Monitor spoolsv.exe for loading DLLs from C:\Windows\System32\spool\drivers\x64\3\ — especially files named nightmare.dll or other unexpected DLL names — as this is the canonical drop path used by PrintNightmare exploits.
  • Alert on spoolsv.exe spawning cmd.exe or whoami with SYSTEM integrity level, as this indicates successful PrintNightmare exploitation and code execution under SYSTEM privileges.
  • Detect outbound network connections from spoolsv.exe, particularly to port 4444/TCP, which is the default Meterpreter callback port and was observed in active PrintNightmare exploitation.
  • Monitor for registry modifications to \REGISTRY\MACHINE\SYSTEM\ControlSet001\Control\Lsa\MSV1_0 following PrintNightmare exploitation, as attackers used this to force NTLMv1 authentication for hash interception.
  • Detect use of certutil.exe to decode files into PE binaries (e.g., certutil -decode 1.txt <output.dll>) as a post-exploitation step observed after PrintNightmare compromise.
  • Exploit code for PrintNightmare has been incorporated into Metasploit and Mimikatz; hunt for Mimikatz artifacts (VHO:Trojan-PSW.Win64.Mimikatz.gen) on hosts where spoolsv.exe showed anomalous behavior.
  • The SharpPrintNightmare PoC uses the Microsoft Print System Asynchronous Remote Protocol (MS-PAR) as an alternative attack vector; network detection should cover both MS-RPRN and MS-PAR traffic to the print spooler.
  • Presence of the PowerShell exploit script cve-2021-1675.ps1 (from the cve-2021-1675-main GitHub repository) on a host is a strong indicator of PrintNightmare exploitation attempt.
  • ·The July 2021 OOB patch for CVE-2021-34527 was bypassed within hours of release under certain conditions; patching alone is insufficient without also addressing Point and Print and printer driver installation policies.
  • ·Palo Alto NGFW Threat Prevention blocks PrintNightmare only when running Applications and Threat content update version 8427 or higher; earlier content versions will not block exploitation.

CVSS provenance

nvdv3.17.8HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
nvdv2.09.3CRITICALAV:N/AC:M/Au:N/C:C/I:C/A:C
vulncheck7.8HIGH
cisa7.8HIGH
vendor_msrc8.8HIGH
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