Bumblebee: New Loader Rapidly Assuming Central Position in Cyber-crime Ecosystem
The attackers also made use of a PowerShell script named cve-2021-34527.ps1 that has previously been linked to Conti’s leaked attack playbook.
CVE-2021-34527 KEVRansomwarePublic exploit High · 8.8 EPSS 99.8%
Microsoft Windows Print Spooler Remote Code Execution Vulnerability
Microsoft · Windows
Summary
A flaw in the Windows Print Spooler service on Microsoft Windows improperly performs privileged file operations, which can allow remote code execution. An attacker with low-privilege authenticated access over the network, requiring no user interaction, could run arbitrary code with SYSTEM privileges and then install programs, view, change or delete data, or create accounts with full user rights.
Official description · NVD
A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. UPDATE July 7, 2021: The security update for Windows Server 2012, Windows Server 2016 and Windows 10, Version 1607 have been released. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. In addition to installing the updates, in order to secure your system, you must confirm that the following registry settings are set to 0 (zero) or are not defined (Note: These registry keys do not exist by default, and therefore are already at the secure setting.), also that your Group Policy setting are correct (see FAQ): HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint NoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting) UpdatePromptSettings = 0 (DWORD) or not defined (default setting) Having NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design. UPDATE July 6, 2021: Microsoft has completed the investigation and has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. See also KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates. Note that the security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527.
Priority scorePatchfirst’s 0 to 100 ranking. It adds points for CISA KEV listing, ransomware use, EPSS, threat reports, public exploit code and CVSS. Every CVE page shows the breakdown. Breakdown
88.1 / 100
- Exploited
- Yes, in CISA KEV
- Reports
- 4
- Tactics
- 2/15
How an attack unfolds
Based on MITRE ATT&CKA public catalogue of the techniques attackers use, maintained by MITRE. Patchfirst uses it to describe what attackers do with a vulnerability. mappings. Select a step to see the evidence.Exploitation timelineDated milestones for a CVE: when it was disclosed, when exploit code became public, when exploitation was confirmed, and when threat reports named it.
First seen exploited the day it was disclosed. Public exploit code (Metasploit) was available 24 days before disclosure.
- Public exploit codeMetasploit24 days before
- Added to CISA KEVknown ransomware use; EU database agrees+4 mo
CISA KEV listing is when exploitation was confirmed, not necessarily the first attack.
MITRE ATT&CKA public catalogue of the techniques attackers use, maintained by MITRE. Patchfirst uses it to describe what attackers do with a vulnerability. techniques
2 TechniqueOne specific attacker behaviour in MITRE ATT&CK, such as T1190 “Exploit Public-Facing Application”. IDs with a dot, like T1059.004, are sub-techniques., grouped by TacticThe attacker’s goal at a stage of an attack in MITRE ATT&CK, such as Initial Access or Persistence. Each technique belongs to one or more tactics. in kill-chain order, 5 cited passages 2ExecutionTA0002
Command and Scripting Interpreter T1059 Medium Confidence (technique links)How sure Patchfirst is that an ATT&CK technique applies to this CVE. High and medium links are shown by default; low ones come from early or generic mappings, text matching, or contradict the CVE’s details.
AI mapping from the description · primary impact
Arbitrary code execution as SYSTEM
could run arbitrary code with SYSTEM privileges
Privilege EscalationTA0004
Exploitation for Privilege Escalation T1068 Medium Confidence (technique links)How sure Patchfirst is that an ATT&CK technique applies to this CVE. High and medium links are shown by default; low ones come from early or generic mappings, text matching, or contradict the CVE’s details.
AI mapping from the description · how it is exploited
Print Spooler privilege flaw enables local escalation; TRAM2 annotated sentence label
improperly performs privileged file operations
Software vulnerabilities, such as PrintNightmare (CVE-2021-1675) and (CVE-2021-34527), may be exploited in an attempt to elevate privileges.
Lower-confidence links (2)
These come from early or generic mappings, text matching, or contradict this CVE’s details (for example a public-facing technique on a bug that needs a user to open a file). Shown for completeness.
- Exploit Public-Facing ApplicationT1190 machine-matched from report text
- Exploitation of Remote ServicesT1210 machine-matched from report text
Detection
5 rules for this CVE · 126 general rules for its techniquesRules for this CVE
5Sigma ruleAn open, vendor-neutral detection rule for log data. Security teams convert Sigma rules into searches for their own SIEM. that reference CVE-2021-34527 directly.- Antivirus PrinterNightmare CVE-2021-34527 Exploit Detectioncriticalstable
- CVE-2021-1675 Print Spooler Exploitation IPC Accesscriticaltest
- PrinterNightmare Mimikatz Driver Namecriticaltest
- Possible PrintNightmare Print Driver Install - CVE-2021-1675mediumstable
- Windows Spooler Service Suspicious Binary Loadinformationaltest
General rules for this CVE’s techniques
These detect the technique in general, not this specific vulnerability.
Exploitation for Privilege EscalationT106831 general rules
- Exploiting CVE-2019-1388criticalstable
- Audit CVE Eventcriticaltest
- HackTool - SysmonEOP Executioncriticaltest
- InstallerFileTakeOver LPE CVE-2021-41379 File Create Eventcriticaltest
- Possible Coin Miner CPU Priority Paramcriticaltest
- Potential CVE-2021-41379 Exploitation Attemptcriticaltest
- Potential SystemNightmare Exploitation Attemptcriticaltest
- Sudo Privilege Escalation CVE-2019-14287 - Builtincriticaltest
Command and Scripting InterpreterT105995 general rules
- HackTool - Sliver C2 Implant Activity Patterncriticaltest
- Lazarus Group Activitycriticaltest
- REvil Kaseya Incident Malware Patternscriticaltest
- Turla Group Lateral Movementcriticaltest
- Windows Defender AMSI Trigger Detectedhighstable
- Windows Defender Threat Detectedhighstable
- Abusable DLL Potential Sideloading From Suspicious Locationhightest
- Add Insecure Download Source To Wingethightest
Sigma rules © SigmaHQ, Detection Rule License 1.1; linked, not reproduced.
What security researchers reported
Named in 4 threat reports4 reportsSymantecUnit 42Cisco Talos+1
Reports are matched by finding the exact id CVE-2021-34527 in their text; nobody has reviewed the match. One passage is shown per report, at most 320 characters, linked to the original.
Vice Society: Profiling a Persistent Threat to the Education Sector
Resources Threat Brief: Windows Print Spooler RCE Vulnerability (CVE-2021-34527 AKA PrintNightmare)Emerging Ransomware Groups: AvosLocker, Hive, HelloKitty, LockBit 2.0Threat Assessment: Zeppelin Ransomware#StopRansomware: Vice…
4 passages name itOriginal (opens in a new tab) ↗
Vice Society leverages PrintNightmare in ransomware attacks
Joe Marshall, and Arnaud Zobec.Executive SummaryAnother threat actor is actively exploiting the so-called PrintNightmare vulnerability (CVE-2021-1675 / CVE-2021-34527) in Windows' print spooler service to spread laterally across a victim's network as part of a recent ransomware attack, according to Cisco Talos…
ICS/OT CYBERSECURITY
Mentions the CVE; no further detail.
Also mentioned in 50 community threat pulses (AlienVault OTX)
Weaker evidencePulses are indicator collections that anyone can publish. A mention is not confirmation of exploitation.
- Actively_Exploited_Kev | Oct 29, 202628 Oct 2026
- Actively_Exploited_Kev | Oct 28, 202627 Oct 2026
- Actively_Exploited_Kev | Oct 27, 202626 Oct 2026
- Actively_Exploited_Kev | Oct 24, 202623 Oct 2026
- Actively_Exploited_Kev | Oct 23, 202622 Oct 2026
- Actively_Exploited_Kev | Oct 22, 202621 Oct 2026
- 44 more on OTX