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AUSCERT External Security Bulletin Redistribution
Cisco AnyConnect Secure Mobility Client for Linux and Mac OS with VPN
Posture (HostScan) Module Shared Library Hijacking Vulnerability
7 October 2021
AusCERT Security Bulletin Summary
Product: AnyConnect Secure Mobility Client
Publisher: Cisco Systems
Operating System: Linux variants
Impact/Access: Root Compromise -- Existing Account
CVE Names: CVE-2021-34788
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Cisco AnyConnect Secure Mobility Client for Linux and Mac OS with VPN Posture
(HostScan) Module Shared Library Hijacking Vulnerability
Advisory ID: cisco-sa-anyconnect-lib-hija-cAFB7x4q
First Published: 2021 October 6 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvz38781
CVE Names: CVE-2021-34788
o A vulnerability in the shared library loading mechanism of Cisco AnyConnect
Secure Mobility Client for Linux and Mac OS could allow an authenticated,
local attacker to perform a shared library hijacking attack on an affected
device if the VPN Posture (HostScan) Module is installed on the AnyConnect
This vulnerability is due to a race condition in the signature verification
process for shared library files that are loaded on an affected device. An
attacker could exploit this vulnerability by sending a series of crafted
interprocess communication (IPC) messages to the AnyConnect process. A
successful exploit could allow the attacker to execute arbitrary code on
the affected device with root privileges. To exploit this vulnerability,
the attacker must have a valid account on the 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 devices that are running a vulnerable release of
Cisco AnyConnect Secure Mobility Client for Linux and Mac OS if the VPN
Posture (HostScan) Module is installed.
Note: The VPN Posture (HostScan) Module should not be confused with the ISE
Posture (SystemScan) Module. The ISE Posture Module is not affected by this
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
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 mobile device operating systems
such as iOS, Android, and Universal Windows Platform
AnyConnect Secure Mobility Client for Linux and Mac OS with only the
ISE Posture (SystemScan) Module installed
AnyConnect Secure Mobility Client for Windows
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
Customers are advised to upgrade to an appropriate fixed software release
as indicated in the following table(s):
Cisco AnyConnect Secure Mobility Client for Linux and Mac First Fixed
OS Release Release
Earlier than 4.10.03104 4.10.03104
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 > AnyConnect Secure
Mobility Client > AnyConnect Secure Mobility Client v4.x .
3. Choose a release from the left pane of the AnyConnect Secure Mobility
Client v4.x page.
The Cisco Product Security Incident Response Team (PSIRT) validates only
the affected and fixed release information that is documented in this
Exploitation and Public Announcements
o The Cisco PSIRT is not aware of any public announcements or malicious use
of the vulnerability that is described in this advisory.
o This vulnerability was found during internal security testing.
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-OCT-06 |
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