Microsoft says that the emergency patch recently released correctly fix the PrintNightmare flaw
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-34527 | PrintNightmare: Remote Code Execution in Microsoft Windows Print Spooler CVE-2021-34527, widely known as 'PrintNightmare', is a remote code execution flaw in the Microsoft Windows Print Spooler service, which improperly performs privileged file operations such as loading printer driver DLLs. An attacker with low-level access who can reach a machine's spooler, for example a domain user able to add a printer connection via Point and Print, can induce the SYSTEM-privileged service to load an attacker-controlled DLL with no user interaction required (CVSS:3.1 vector AV:N/AC:L/PR:L/UI:N). Successful exploitation yields arbitrary code execution as SYSTEM, letting the attacker install programs, view, change or delete data, and create new accounts with full user rights, effectively achieving complete host compromise. The flaw affects all supported Windows client and server releases in the CISA data, Windows 10 from 1507 through 22H2, Windows 11, Windows RT 8.1, and Windows Server 2008, 2012 and 2016, wherever the Print Spooler service is running. Exploitation is confirmed in the wild: the bug was added to CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 with known ransomware use, the FBI and CISA have warned of Russian actors exploiting it, and EPSS places the 30-day exploitation probability at 99.8%. Do: Install the July 2021 security updates immediately, released July 6, 2021 with additional updates on July 7 for Windows Server 2012, Windows Server 2016 and Windows 10 version 1607, and review KB5005010 for restricting installation of new printer drivers after applying the July 6 updates. Where patching is delayed, disable the Print Spooler service on hosts that do not need printing or restrict Point and Print, and verify that NoWarningNoElevationOnInstall and UpdatePromptSettings under HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint are set to 0 or not defined (these keys do not exist by default, which is the secure state; NoWarningNoElevationOnInstall = 1 makes the system vulnerable by design). Prioritize domain controllers and servers with exposed spoolers, and hunt… | 8.8 | 100% | KEV ransomware PoC ×3 |
| masshundreds of millions of Windows systems (order of magnitude 10^8) |
Full article513 words · extracted from securityaffairs.com · click to collapse
Microsoft confirmed that the emergency security updates (KB5005010) correctly address the PrintNightmare Print Spooler vulnerability (CVE-2021-34527).
Microsoft says that the emergency security patches released early this week correctly address the PrintNightmare Print Spooler vulnerability (CVE-2021-34527) for all supported Windows versions.
Immediately after the release of the updates (KB5004945) multiple researchers questioned its efficiency and explained that the updates don’t fully address the vulnerability.
Researchers have demonstrated that it is possible to bypass the emergency patch to achieve remote code execution and local privilege escalation on systems that have installed it.
Shortly after the release of the patch, the popular researcher Matthew Hickey noticed that the fix is incomplete and that threat actors and malware can still locally exploit the vulnerability to gain SYSTEM privileges.
The Microsoft fix released for recent #PrintNightmare vulnerability addresses the remote vector – however the LPE variations still function. These work out of the box on Windows 7, 8, 8.1, 2008 and 2012 but require Point&Print configured for Windows 2016,2019,10 & 11(?). 🤦♂️ https://t.co/PRO3p99CFo
— hackerfantastic.x (@hackerfantastic) July 6, 2021
The failure of the Microsoft update was also reported by Will Dormann, a vulnerability analyst for CERT/CC.
Other researchers started testing the patch and demonstrated that it was possible to entirely bypass the fix to achieve both RCE and local privilege escalation (LPE).
The expert Benjamin Delpy, also known for having developed the popular Mimikatz tool, discovered that when the Point and Print policy is enabled, attackers could bypass the patch to achieve Remote Code Execution.
The clarified guidance for CVE-2021-34527 Windows Print Spooler Vulnerability published by Microsoft encourages customers to update as soon as possible.
“Our investigation has shown that the OOB security update is working as designed and is effective against the known printer spooling exploits and other public reports collectively being referred to as PrintNightmare. All reports we have investigated have relied on the changing of default registry setting related to Point and Print to an insecure configuration.” states the guidance published by Microsoft Security Response Center.
The IT giant recommends that customers follow the following steps immediately:
- In ALL cases, apply the CVE-2021-34527 security update. The update will not change existing registry settings
- After applying the security update, review the registry settings documented in the CVE-2021-34527 advisory
- If the registry keys documented do not exist, no further action is required
- If the registry keys documented exist, in order to secure your system, you must confirm that the following registry keys are set to 0 (zero) or are not present:
- 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)
Users that cannot immediately install the security updates are recommended to disable the Windows Print Spooler service to mitigate the PrintNightmare vulnerability temporarily.
The CERT Coordination Center (CERT/CC) has also published an alert that includes instructions on stopping and disabling the service in a separate Vulnerability Note.
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Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/119896/security/microsoft-fixed-printnightmare-flaw.html