Quick look at CVE-2021-1675 & CVE-2021
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 article482 words · extracted from securelist.com · click to collapse
Summary
Last week Microsoft warned Windows users about vulnerabilities in the Windows Print Spooler service – CVE-2021-1675 and CVE-2021-34527 (also known as PrintNightmare). Both vulnerabilities can be used by an attacker with a regular user account to take control of a vulnerable server or client machine that runs the Windows Print Spooler service. This service is enabled by default on all Windows clients and servers, including domain controllers.
Kaspersky products protect against attacks leveraging these vulnerabilities. The following detection names are used:
- HEUR:Exploit.Win32.CVE-2021-1675.*
- HEUR:Exploit.Win32.CVE-2021-34527.*
- HEUR:Exploit.MSIL.CVE-2021-34527.*
- HEUR:Exploit.Script.CVE-2021-34527.*
- HEUR:Trojan-Dropper.Win32.Pegazus.gen
- PDM:Exploit.Win32.Generic
- PDM:Trojan.Win32.Generic
- Exploit.Win32.CVE-2021-1675.*
- Exploit.Win64.CVE-2021-1675.*
Our detection logic is also successfully blocks attack technique from the latest Mimikatz framework v. 2.2.0-20210707.
We are closely monitoring the situation and improving generic detection of these vulnerabilities using our Behavior Detection and Exploit Prevention components. As part of our Managed Detection and Response service Kaspersky SOC experts are able to detect exploitation of these vulnerabilities, investigate such attacks and report to customers.
Technical details
CVE-2021-34527
When using RPC protocols to add a new printer (RpcAsyncAddPrinterDriver [MS-PAR] or RpcAddPrinterDriverEx [MS-RPRN]) a client has to provide multiple parameters to the Print Spooler service:
- pDataFile – a path to a data file for this printer;
- pConfigFile – a path to a configuration file for this printer;
- pDriverPath – a path to a driver file that’s used by this printer while it’s working.
The service makes several checks to ensure pDataFile and pDriverPath are not UNC paths, but there is no corresponding check for pConfigFile, meaning the service will copy the configuration DLL to the folder %SYSTEMROOT%\system32\spool\drivers\x64\3\ (on x64 versions of the OS).
Now, if the Windows Print Spooler service tries to add a printer again, but this time sets pDataFile to the copied DLL path (from the previous step), the print service will load this DLL because its path is not a UNC path, and the check will be successfully passed. These methods can be used by a low-privileged account, and the DLL is loaded by the NT AUTHORITY\SYSTEM group process.
CVE-2021-1675
The local version of PrintNightmare uses the same method for exploitation as CVE-2021-34527, but there’s a difference in the entrypoint function (AddPrinterDriverEx). This means an attacker can place a malicious DLL in any locally accessible directory to run the exploit.
Mitigations
Kaspersky experts anticipate a growing number of exploitation attempts to gain access to resources inside corporate perimeters accompanied by a high risk of ransomware infection and data theft.
Therefore, it is strongly recommended to follow Microsoft guidelines and apply the latest security updates for Windows.
Quoting Microsoft (as of July 7th, 2021):
“Due to the possibility for exposure, domain controllers and Active Directory admin systems need to have the Print spooler service disabled. The recommended way to do this is using a Group Policy Object (GPO).
While this security assessment focuses on domain controllers, any server is potentially at risk to this type of attack.”
Text extracted automatically; images, tables and formatting may be missing. Original: https://securelist.com/quick-look-at-cve-2021-1675-cve-2021-34527-aka-printnightmare/103123/