Microsoft's Emergency Patch Fails to Fully Fix PrintNightmare RCE Vulnerability
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-1675 | Remote Code Execution in Microsoft Windows Print Spooler (PrintNightmare) CVE-2021-1675 is a code execution flaw in the Windows Print Spooler service affecting the listed Windows 10, 7, 8.1, RT 8.1 and Windows Server editions. It is triggered through print operations processed by the spooler, notably print driver handling; the public PoC demonstrates DLL injection into the spooler, allowing an attacker to run arbitrary code with the privileges of the spooler service, typically SYSTEM. Successful exploitation yields full system compromise: installing programs, viewing or deleting data, creating accounts, and lateral movement into domains, which is why it has been widely used as a ransomware entry vector. Any Windows system with the Print Spooler service enabled is exposed, and the service runs by default on servers, domain controllers, and most workstations. Exploitation is confirmed in the wild: a public PoC is available, the flaw was weaponized by the Magniber and Vice Society ransomware groups, it was added to CISA KEV on 2021-11-03 with known ransomware use, and Microsoft issued out-of-band fixes after it was being exploited in the wild. Do: Apply Microsoft's out-of-band security updates immediately on all affected Windows client and server systems (per CISA KEV required action), prioritizing domain controllers and print/file servers. As an interim mitigation, disable the Print Spooler service on hosts that do not need printing (e.g., domain controllers) and restrict RPC/network access to the spooler on systems that must keep it running. Check for compromise by looking for unexpected DLL or driver files loaded by the spooler, spoolsv.exe spawning unusual child processes, and ransomware indicators given documented Magniber and Vice Society abuse. | 7.8 | 86% | KEV ransomware PoC |
| masshundreds of millions of Windows endpoints and servers (Print Spooler runs by default across the 1B+ device Windows installed base) | |
| 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 article640 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananJul 08, 2021
Even as Microsoft expanded patches for the so-called PrintNightmare vulnerability for Windows 10 version 1607, Windows Server 2012, and Windows Server 2016, it has come to light that the fix for the remote code execution exploit in the Windows Print Spooler service can be bypassed in certain scenarios, effectively defeating the security protections and permitting attackers to run arbitrary code on infected systems.
On Tuesday, the Windows maker issued an emergency out-of-band update to address CVE-2021-34527 (CVSS score: 8.8) after the flaw was accidentally disclosed by researchers from Hong Kong-based cybersecurity firm Sangfor late last month, at which point it emerged that the issue was different from another bug — tracked as CVE-2021-1675 — that was patched by Microsoft on June 8.
"Several days ago, two security vulnerabilities were found in Microsoft Windows' existing printing mechanism," Yaniv Balmas, head of cyber research at Check Point, told The Hacker News. "These vulnerabilities enable a malicious attacker to gain full control on all windows environments that enable printing."
"These are mostly working stations but, at times, this relates to entire servers that are an integral part of very popular organizational networks. Microsoft classified these vulnerabilities as critical, but when they were published they were able to fix only one of them, leaving the door open for explorations of the second vulnerability," Balmas added.
PrintNightmare stems from bugs in the Windows Print Spooler service, which manages the printing process inside local networks. The main concern with the threat is that non-administrator users had the ability to load their own printer drivers. This has now been rectified.
"After installing this [update] and later Windows updates, users who are not administrators can only install signed print drivers to a print server," Microsoft said, detailing the improvements made to mitigate the risks associated with the flaw. "Administrator credentials will be required to install unsigned printer drivers on a printer server going forward."
Post the update's release, CERT/CC vulnerability analyst Will Dormann cautioned that the patch "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," thereby allowing attackers to abuse the latter to gain SYSTEM privileges on vulnerable systems.
Now, further testing of the update has revealed that exploits targeting the flaw could bypass the remediations entirely to gain both local privilege escalation and remote code execution. To achieve this, however, a Windows policy called 'Point and Print Restrictions' must be enabled (Computer Configuration\Policies\Administrative Templates\Printers: Point and Print Restrictions), using which malicious printer drivers could be potentially installed.
"Note that the Microsoft update for CVE-2021-34527 does not effectively prevent exploitation of systems where the Point and Print NoWarningNoElevationOnInstall is set to 1," Dormann said Wednesday. Microsoft, for its part, explains in its advisory that "Point and Print is not directly related to this vulnerability, but the technology weakens the local security posture in such a way that exploitation will be possible."
While Microsoft has recommended the nuclear option of stopping and disabling the Print Spooler service, an alternative workaround is to enable security prompts for Point and Print, and limit printer driver installation privileges to administrators alone by configuring the "RestrictDriverInstallationToAdministrators" registry value to prevent regular users from installing printer drivers on a print server.
UPDATE: In response to CERT/CC's report, Microsoft said on Thursday:
"Our investigation has shown that the OOB [out-of-band] 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."
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Text extracted automatically; images, tables and formatting may be missing. Original: https://thehackernews.com/2021/07/microsofts-emergency-patch-fails-to.html