Microsoft Issues Emergency Patch for Critical Windows PrintNightmare Vulnerability
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 article355 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananJul 07, 2021
Microsoft has shipped an emergency out-of-band security update to address a critical zero-day vulnerability — known as "PrintNightmare" — that affects the Windows Print Spooler service and can permit remote threat actors to run arbitrary code and take over vulnerable systems.
Tracked as CVE-2021-34527 (CVSS score: 8.8), the remote code execution flaw impacts all supported editions of Windows. Last week, the company warned it had detected active exploitation attempts targeting the vulnerability.
"The Microsoft Windows Print Spooler service fails to restrict access to functionality that allows users to add printers and related drivers, which can allow a remote authenticated attacker to execute arbitrary code with SYSTEM privileges on a vulnerable system," the CERT Coordination Center said of the issue.
It's worth noting that PrintNightmare includes both remote code execution and a local privilege escalation vector that can be abused in attacks to run commands with SYSTEM privileges on targeted Windows machines.
"The Microsoft update for CVE-2021-34527 only appears to address the Remote Code Execution (RCE via SMB and RPC) variants of the PrintNightmare, and not the Local Privilege Escalation (LPE) variant," CERT/CC vulnerability analyst Will Dormann said.
This effectively means that the incomplete fix could still be used by a local adversary to gain SYSTEM privileges. As workarounds, Microsoft recommends stopping and disabling the Print Spooler service or turning off inbound remote printing through Group Policy to block remote attacks.
Given the criticality of the flaw, the Windows maker has issued patches for:
- Windows Server 2019
- Windows Server 2012 R2
- Windows Server 2008
- Windows 8.1
- Windows RT 8.1, and
- Windows 10 (versions 21H1, 20H2, 2004, 1909, 1809, 1803, and 1507)
Microsoft has even taken the unusual step of issuing the fix for Windows 7, which officially reached the end of support as of January 2020.
The update, however, does not include Windows 10 version 1607, Windows Server 2012, or Windows Server 2016, for which the Redmond-based company stated patches will be released in the forthcoming days.
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