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AUSCERT External Security Bulletin Redistribution
ESB-2023.6368
Cisco Adaptive Security Appliance Software and Firepower Threat Defense
Software Remote Access VPN Denial of Service Vulnerability
2 November 2023
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco Adaptive Security Appliance Software
Firepower Threat Defense Software
Publisher: Cisco Systems
Operating System: Cisco
Resolution: Patch/Upgrade
CVE Names: CVE-2023-20095
Original Bulletin:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-webvpn-dos-3GhZQBAS
Comment: CVSS (Max): 8.6 CVE-2023-20095 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H)
CVSS Source: Cisco Systems
Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
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Cisco Adaptive Security Appliance Software and Firepower Threat Defense
Software Remote Access VPN Denial of Service Vulnerability
Priority: High
Advisory ID: cisco-sa-asa-webvpn-dos-3GhZQBAS
First Published: 2023 November 1 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCwb63827
CVE Names: CVE-2023-20095
Summary
o A vulnerability in the remote access VPN feature of Cisco Adaptive Security
Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
could allow an unauthenticated, remote attacker to cause a denial of
service (DoS) condition on an affected device.
This vulnerability is due to improper handling of HTTPS requests. An
attacker could exploit this vulnerability by sending crafted HTTPS requests
to an affected system. A successful exploit could allow the attacker to
cause resource exhaustion, resulting in a DoS condition.
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:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-webvpn-dos-3GhZQBAS
This advisory is part of the November 2023 release of the Cisco ASA, FTD,
and FMC Security Advisory Bundled publication. For a complete list of the
advisories and links to them, see Cisco Event Response: November 2023
Semiannual Cisco ASA, FMC, and FTD Software Security Advisory Bundled
Publication .
Affected Products
o Vulnerable Products
This vulnerability affects the following Cisco products:
ASA Software when it has Cisco AnyConnect Remote Access VPN or
Clientless SSL VPN enabled
FTD Software when it has Cisco AnyConnect Remote Access VPN enabled
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine the Cisco ASA Software Configuration
To determine whether Cisco ASA Software has a vulnerable feature enabled,
use the show-running-config CLI command.
In the following table, the left column lists Cisco ASA Software features
that are vulnerable. The right column indicates the basic configuration for
each feature from the show running-config CLI command. If a device is
running a vulnerable release and has one of these features enabled, it is
vulnerable:
Cisco ASA Software Feature Vulnerable Configuration
AnyConnect Internet Key Exchange crypto ikev2 enable client-services port
Version 2 (IKEv2) Remote Access
(with client services)
webvpn
AnyConnect SSL VPN enable
Clientless SSL VPN webvpn
enable
Determine the Cisco FTD Software Configuration
To determine whether Cisco FTD Software has a vulnerable feature enabled,
use the show-running-config CLI command.
In the following table, the left column lists Cisco FTD Software features
that are vulnerable. The right column indicates the basic configuration for
each feature from the show running-config CLI command. If a device is
running a vulnerable release and has one of these features enabled, it is
vulnerable:
Cisco FTD Feature Vulnerable Configuration
AnyConnect IKEv2 Remote Access crypto ikev2 enable client-services port
(with client services) ^1,2
AnyConnect SSL VPN ^1,2 webvpn
enable
1. Remote Access VPN features were introduced in Cisco FTD Software Release
6.2.2.
2. Remote Access VPN features can be enabled using Devices > VPN > Remote
Access in Cisco Firepower Management Center (FMC) or using Device > Remote
Access VPN in Cisco Firepower Device Manager (FDM).
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 Cisco Firepower
Management Center (FMC) Software.
Cisco has also confirmed that this vulnerability does not affect devices
that have remote access VPN services configured to accept only Cisco
AnyConnect IKEv2 Remote Access VPNs that have client services disabled.
Workarounds
o There are no workarounds that address this vulnerability.
Fixed Software
o Cisco has released free software updates that address the vulnerability
described in this advisory. Customers with service contracts that entitle
them to regular software updates should obtain security fixes through their
usual update channels.
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 software license:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.html
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.
The Cisco Support and Downloads page on Cisco.com provides information
about licensing and downloads. This page can also display customer device
support coverage for customers who use the My Devices tool.
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
upgrade solution.
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
providers.
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
/en/us/support/web/tsd-cisco-worldwide-contacts.html
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
upgrade.
Cisco ASA, FMC, and FTD Software
To help customers determine their exposure to vulnerabilities in Cisco ASA,
FMC, and FTD Software, Cisco provides the Cisco Software Checker . This
tool identifies any Cisco security advisories that impact a specific
software release and the earliest release that fixes the vulnerabilities
that are described in each advisory ("First Fixed"). If applicable, the
tool also returns the earliest release that fixes all the vulnerabilities
that are described in all the advisories that the Software Checker
identifies ("Combined First Fixed").
To use the tool, go to the Cisco Software Checker page and follow the
instructions. Alternatively, use the following form to search for
vulnerabilities that affect a specific software release. To use the form,
follow these steps:
1. Choose which advisories the tool will search-all advisories, only
advisories with a Critical or High Security Impact Rating (SIR) , or
only this advisory.
2. Choose the appropriate software.
3. Choose the appropriate platform.
4. Enter a release number-for example, 9.16.2.11 for Cisco ASA Software or
6.6.7 for Cisco FTD Software.
5. Click Check .
[2 ] [ ] [Critical,High,Medium]
[Only this advisory ] [Cisco ASA Software]
[Any Platform ]
[ ] [Check]
For instructions on upgrading your FTD device, see Cisco Firepower
Management Center Upgrade Guide .
Additional Resources
For help determining the best Cisco ASA, FTD, or FMC Software release, see
the following Recommended Releases documents. If a security advisory
recommends a later release, Cisco recommends following the advisory
guidance.
Cisco ASA Compatibility
Cisco Secure Firewall ASA Upgrade Guide
Cisco Secure Firewall Threat Defense Compatibility Guide
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.
Source
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.
Subscribe to Cisco Security Notifications
o Subscribe
Related to This Advisory
o Cisco Event Response: November 2023 Cisco ASA, FMC, and FTD Software
Security Advisory Bundled Publication
URL
o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-webvpn-dos-3GhZQBAS
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2023-NOV-01 |
+----------+---------------------------+----------+--------+--------------+
Legal Disclaimer
o THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND
OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT
OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES
THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information
or contain factual errors. The information in this document is intended for
end users of Cisco products.
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