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AUSCERT External Security Bulletin Redistribution
Cisco AnyConnect Secure Mobility Client for Windows with VPN Posture
(HostScan) Module DLL Hijacking Vulnerability
18 February 2021
AusCERT Security Bulletin Summary
Product: Cisco AnyConnect Secure Mobility Client for Windows
Publisher: Cisco Systems
Operating System: Windows
Impact/Access: Administrator Compromise -- Existing Account
Execute Arbitrary Code/Commands -- Existing Account
CVE Names: CVE-2021-1366
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Cisco AnyConnect Secure Mobility Client for Windows with VPN Posture (HostScan)
Module DLL Hijacking Vulnerability
Advisory ID: cisco-sa-anyconnect-dll-hijac-JrcTOQMC
First Published: 2021 February 17 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvv64243
CVE Names: CVE-2021-1366
o A vulnerability in the interprocess communication (IPC) channel of Cisco
AnyConnect Secure Mobility Client for Windows could allow an authenticated,
local attacker to perform a DLL hijacking attack on an affected device if
the VPN Posture (HostScan) Module is installed on the AnyConnect client.
This vulnerability is due to insufficient validation of resources that are
loaded by the application at run time. An attacker could exploit this
vulnerability by sending a crafted IPC message to the AnyConnect process. A
successful exploit could allow the attacker to execute arbitrary code on
the affected machine with SYSTEM privileges. To exploit this vulnerability,
the attacker needs valid credentials on the Windows system.
Cisco has released software updates that address this vulnerability. There
are no workarounds that address this vulnerability.
This advisory is available at the following link:
o Vulnerable Products
This vulnerability affects Cisco AnyConnect Secure Mobility Client for
Windows releases earlier than Release 4.9.05042 that have the VPN Posture
(HostScan) Module installed.
Note: The VPN Posture (HostScan) Module should not be confused with the ISE
Posture Module. The ISE Posture Module is not affected by this
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following
AnyConnect Secure Mobility Client for Linux
AnyConnect Secure Mobility Client for Mac OS
AnyConnect Secure Mobility Client for mobile device operating systems
such as iOS, Android, and Universal Windows Platform
AnyConnect Secure Mobility Client for Windows with only the ISE Posture
o There are no workarounds that address this vulnerability.
o Cisco has released free software updates that address the vulnerability
described in this advisory. Customers may only install and expect support
for software versions and feature sets for which they have purchased a
license. By installing, downloading, accessing, or otherwise using such
software upgrades, customers agree to follow the terms of the Cisco
Additionally, customers may only download software for which they have a
valid license, procured from Cisco directly, or through a Cisco authorized
reseller or partner. In most cases this will be a maintenance upgrade to
software that was previously purchased. Free security software updates do
not entitle customers to a new software license, additional software
feature sets, or major revision upgrades.
When considering software upgrades , customers are advised to regularly
consult the advisories for Cisco products, which are available from the
Cisco Security Advisories page , to determine exposure and a complete
In all cases, customers should ensure that the devices to be upgraded
contain sufficient memory and confirm that current hardware and software
configurations will continue to be supported properly by the new release.
If the information is not clear, customers are advised to contact the Cisco
Technical Assistance Center (TAC) or their contracted maintenance
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service
contract and customers who make purchases through third-party vendors but
are unsuccessful in obtaining fixed software through their point of sale
should obtain upgrades by contacting the Cisco TAC: https://www.cisco.com/c
Customers should have the product serial number available and be prepared
to provide the URL of this advisory as evidence of entitlement to a free
Cisco fixed this vulnerability in Cisco AnyConnect Secure Mobility Client
for Windows releases 4.9.05042 and later.
To download the software from the Software Center on Cisco.com, do the
1. Click Browse all .
2. Choose Security > VPN and Endpoint Security Clients > Cisco VPN Clients
> AnyConnect Secure Mobility Client > AnyConnect Secure Mobility Client
3. Choose a release from the left pane of the AnyConnect Secure Mobility
Client v4.x page.
Exploitation and Public Announcements
o The Cisco Product Security Incident Response Team (PSIRT) is not aware of
any public announcements or malicious use of the vulnerability that is
described in this advisory.
o Cisco would like to thank Marcos Accossatto and Pablo Zurro of Core
Security for reporting this vulnerability.
Cisco Security Vulnerability Policy
o To learn about Cisco security vulnerability disclosure policies and
publications, see the Security Vulnerability Policy . This document also
contains instructions for obtaining fixed software and receiving security
vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2021-FEB-17 |
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