ASB-2021.0123.3 – UPDATE ALERT [Win] Microsoft Print Spooler: Multiple vulnerabilities

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AUSCERT Security Bulletin

ASB-2021.0123.3
Windows Print Spooler Remote Code Execution Vulnerability
7 July 2021

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AusCERT Security Bulletin Summary
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Product: Microsoft Print Spooler
Operating System: Windows
Impact/Access: Administrator Compromise — Existing Account
Execute Arbitrary Code/Commands — Existing Account
Resolution: Patch/Upgrade
CVE Names: CVE-2021-34527 CVE-2021-1675
Reference: ASB-2021.0116
ASB-2021.0115

Revision History: July 7 2021: Microsoft revised advisory to announce patches are now available for CVE-2021-34527
July 5 2021: Microsoft revised advisory to update the FAQ, add a mitigation, and add CVSS score
July 2 2021: Initial Release

OVERVIEW

Microsoft has released an out-of-band critical update to address a
Windows Print Spooler Remote Code Execution Vulnerability.
Microsoft has assigned CVE-2021-34527 to this vulnerability and
acknowledges it has been referred to publicly as PrintNightmare.[1]

This vulnerability has received significant media attention in the past day.
[2] [3] [4] [5]

IMPACT

Microsoft has stated the following:

“Microsoft is aware of and investigating a remote code execution
vulnerability that affects Windows Print Spooler and has assigned
CVE-2021-34527 to this vulnerability. This is an evolving situation
and we will update the CVE as more information is available.

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.

An attack must involve an authenticated user calling RpcAddPrinterDriverEx().”
[1]

= Update by Microsoft 20210703 =
Microsoft updated advisory to confirm that client systems and non domain
controller member servers are affected under certain specified conditions. [1]

MITIGATION

Microsoft recommends applying the latest security updates released
on June 8 AND determining if the Print Spooler service is running
and either disabling it or disabling inbound remote printing through
Group Policy. [1]

Microsoft acknowledges this vulnerability is similar to but distinct
from the recent Print Spooler vulnerability reported as
CVE-2021-1675 and addressed by the June 2021 security updates, and
that they are still investigating the issue and will update the page
as more information becomes available. [1]

= Update by Microsoft 20210703 = Microsoft updated advisory to
include further mitigation options as an alternative to disabling
printing which involves modifying various group memberships, but
notes this does risk compatibility problems. [1]

= Update by Microsoft 20210706 = Microsoft updated advisory to
announce an update is being released for several versions of
Windows to address this vulnerability. Updates are not yet available
for Windows 10 version 1607, Windows Server 2016, or Windows Server
2012. Microsoft have stated that security updates for these versions
of Windows will be released at a later date. Microsoft advise the
updates should be applied immediately. [1]

REFERENCES

[1] Windows Print Spooler Remote Code Execution Vulnerability
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34527

[2] ‘PrintNightmare’ Stuxnet-style zero-day
https://www.itnews.com.au/news/researchers-accidentally-publish-printnightmare-stuxnet-style-zero-day-566767

[3] Public Windows PrintNightmare 0-day exploit allows domain takeover
https://www.bleepingcomputer.com/news/security/public-windows-printnightmare-0-day-exploit-allows-domain-takeover/

[4] Researchers accidentally release exploit code for new Windows
‘zero-day’ bug PrintNightmare
https://portswigger.net/daily-swig/researchers-accidentally-release-exploit-code-for-new-windows-zero-day-bug-printnightmare

[5] PrintNightmare, Critical Windows Print Spooler Vulnerability
https://us-cert.cisa.gov/ncas/current-activity/2021/06/30/printnightmare-critical-windows-print-spooler-vulnerability

AusCERT has made every effort to ensure that the information contained
in this document is accurate. However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation’s site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

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Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for member emergencies only.
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