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AUSCERT External Security Bulletin Redistribution
ESB-2020.4048
Citrix Virtual Apps and Desktops Security Update
13 November 2020
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AusCERT Security Bulletin Summary
---------------------------------
Product: XenDesktop 7.6
XenDesktop 7.15
Citrix Virtual apps and desktop 7 1912 LTSR Cumulative Update 1
Citrix Virtual Apps and Desktops
Publisher: Citrix
Operating System: Citrix XenServer
Windows
Impact/Access: Execute Arbitrary Code/Commands -- Existing Account
Increased Privileges -- Existing Account
Resolution: Patch/Upgrade
CVE Names: CVE-2020-8270 CVE-2020-8269
Original Bulletin:
https://support.citrix.com/article/CTX285059
- --------------------------BEGIN INCLUDED TEXT--------------------
Citrix Virtual Apps and Desktops Security Update
Reference: CTX285059
Category : High
Created : 10 Nov 2020
Modified : 10 Nov 2020
Applicable Products
o XenDesktop 7.6
o XenDesktop 7.15
o Citrix Virtual apps and desktop 7 1912 LTSR Cumulative Update 1
o Citrix Virtual Apps and Desktops
Description of Problem
Vulnerabilities have been identified in Citrix Virtual Apps and Desktops that
could, if exploited,result in:
o A user who has access to a Windows Virtual Desktop being able to escalate their
privilege level on that Windows Virtual Desktop to SYSTEM.
o Remote compromise of a Windows Virtual Desktop which has Windows file sharing
(SMB) enabled.
These vulnerabilities have the following identifiers:
+-------------+--------------------------+------------------+-----------------------+
|CVE ID |Description |Vulnerability Type|Pre-conditions |
+-------------+--------------------------+------------------+-----------------------+
| |An unprivileged Windows | |The attacker must be |
| |user on the |CWE-269: Improper |an authenticated |
|CVE-2020-8269|VDA can perform arbitrary |Privilege |user on the Windows |
| |command |Management |VDA with write access |
| |execution as SYSTEM | |to the C:\directory |
+-------------+--------------------------+------------------+-----------------------+
| | |CWE-78: Improper |The attacker must be |
| |An unprivileged Windows |Neutralization of |an authenticated |
| |user on the |Special Elements |user on the Windows |
|CVE-2020-8270|VDA or a SMB user can |used in an OS |VDA or be authenticated|
| |perform arbitrary command |Command ('OS |to Windows SMB |
| |execution as SYSTEM |Command |service running |
| | |Injection') |on the VDA |
+-------------+--------------------------+------------------+-----------------------+
The vulnerabilities affect the following supported versions of Citrix Virtual Apps
and Desktops:
o Citrix Virtual Apps and Desktops 2006 and earlier versions
o Citrix Virtual Apps and Desktops 1912 LTSR CU1 and earlier versions of 1912
LTSR
o Citrix XenApp/XenDesktop7.15 LTSR CU6 and earlier versions of 7.15 LTSR
o Citrix XenApp/XenDesktop7.6 LTSR CU8 and earlier versions of 7.6 LTSR
Please note that CitrixXenApp/XenDesktop 7.6 LTSR is not affected
by CVE-2020-8270.
Mitigating Factors
CVE-2020-8269- This issue is only exploitable if low-privilege users have been
granted permission to write files to the C:\ directory. This permission is not
default in Windows and Citrix recommends that users are only granted the
permissions they require.
CVE-2020-8270 - A remote compromise is only possible when Windows file sharing
(SMB) is enabled on the Windows Virtual Desktop. If authentication is required
for SMB then an attacker must also be able to authenticate in order to remotely
compromise the Virtual Desktop.
What Customers Should Do
The issues have been addressed in the following versions of Citrix Virtual Apps
and Desktops:
o Citrix Virtual Apps and Desktops 2009 or later
o Citrix Virtual Apps and Desktops 1912 LTSRCU1 hotfixes CTX285870,CTX285871,
CTX285872 and CTX286120, and later cumulative updates
o Citrix XenApp/XenDesktop7.15 LTSR CU6 hotfixes
CTX285341,CTX285342 and CTX285344, and later cumulative updates
o Citrix XenApp/XenDesktop7.6 LTSR CU9 and later cumulative updates
Citrix strongly recommends that customers upgrade to a fixed version as soon as
possible.
The latest versions of Citrix Virtual Apps and
Desktops are available from the following location:
https://www.citrix.com/en-gb/downloads/citrix-virtual-apps-and-desktops/
Hot fixes to address the issues in Citrix Virtual Apps and Desktops 1912 LTSR
and Citrix XenApp/XenDesktop7.15 LTSR can be downloaded from the following locations:
Citrix Virtual Apps and Desktops1912 CU1
CTX285870 - https://support.citrix.com/article/CTX285870
CTX285871 - https://support.citrix.com/article/CTX285871
CTX285872 - https://support.citrix.com/article/CTX285872
CTX286120 - https://support.citrix.com/article/CTX286120
Citrix XenApp /XenDesktop7.15 CU6
CTX285341 - https://support.citrix.com/article/CTX285341
CTX285342 - https://support.citrix.com/article/CTX285342
CTX285344- https://support.citrix.com/article/CTX285344
Customers should ensure they have installed the latest cumulative update and
then apply all hotfixes for that version.
Acknowledgements
Citrix would like to thank HannayAl-Mohanna of F-Secure Consulting and Michael
Garrison of State Farm Information Security for working with us to protect Citrix
customers.
Changelog
+--------------------------+--------------------------------------------------+
|Date |Change |
+--------------------------+--------------------------------------------------+
|2020-11-10 |Initial Publication |
+--------------------------+--------------------------------------------------+
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