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AUSCERT External Security Bulletin Redistribution
ESB-2023.1717
Cisco Adaptive Security Appliance Software and Firepower
Threat Defense Software Low-Entropy Keys Vulnerability
23 March 2023
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AusCERT Security Bulletin Summary
---------------------------------
Product: Adaptive Security Appliance Software
Firepower Threat Defense Software
Publisher: Cisco Systems
Operating System: Cisco
Resolution: Patch/Upgrade
CVE Names: CVE-2023-20107
Original Bulletin:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa5500x-entropy-6v9bHVYP
Comment: CVSS (Max): 5.3 CVE-2023-20107 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)
CVSS Source: Cisco Systems
Calculator: https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
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Cisco Adaptive Security Appliance Software and Firepower Threat Defense
Software Low-Entropy Keys Vulnerability
Priority: Medium
Advisory ID: cisco-sa-asa5500x-entropy-6v9bHVYP
First Published: 2023 March 22 16:00 GMT
Version 1.0: Final
Workarounds: Yes
Cisco Bug IDs: CSCvm90511
CVE Names: CVE-2023-20107
CVSS Score:
5.3 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:X/RL:X/RC:X
Summary
o A vulnerability in the deterministic random bit generator (DRBG), also
known as pseudorandom number generator (PRNG), in Cisco Adaptive Security
Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
for Cisco ASA 5506-X, ASA 5508-X, and ASA 5516-X Firewalls could allow an
unauthenticated, remote attacker to cause a cryptographic collision,
enabling the attacker to discover the private key of an affected device.
This vulnerability is due to insufficient entropy in the DRBG for the
affected hardware platforms when generating cryptographic keys. An attacker
could exploit this vulnerability by generating a large number of
cryptographic keys on an affected device and looking for collisions with
target devices. A successful exploit could allow the attacker to
impersonate an affected target device or to decrypt traffic secured by an
affected key that is sent to or from an affected target device.
Cisco has released software updates that address this vulnerability. There
are workarounds that address this vulnerability for some affected
configurations.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa5500x-entropy-6v9bHVYP
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected the following Cisco
products if they were running a Cisco ASA Software release earlier than
Release 9.12.1 ^ 1 or a Cisco FTD Software release earlier than Release
6.4.0 ^ 1 and had features that use ECDSA or RSA keys enabled:
ASA 5506-X Security Appliances
ASA 5506H-X Security Appliances
ASA 5506W-X Security Appliances
ASA 5508-X Security Appliances
ASA 5516-X Security Appliances
1. Enhancements to the entropy source in the DRBG that were put in place as
result of following the robust Cisco secure development lifecycle (SDL)
process prevent this issue from happening in Cisco ASA Software Releases
9.12.1 and later and Cisco FTD Software Releases 6.4.0 and later.
Note: Devices that are running a fixed release of Cisco ASA Software or
Cisco FTD Software may also be affected by this vulnerability if they are
configured with an ECDSA or RSA key pair that has been generated while
running an affected release. If there is doubt, Cisco recommends
regenerating all ECDSA and RSA key pairs that are configured on the device.
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
ASA Software
In the following table, the left column lists the most common Cisco ASA
features that are potentially vulnerable. The right column indicates the
basic configuration for the feature from the show running-config CLI
command, if it can be determined.
Cisco ASA Feature Possible Vulnerable Configuration
Adaptive Security Device Manager http server enable
(ASDM) ^1 http
AnyConnect SSL VPN webvpn
enable
Cisco Security Manager ^1 http server enable
http
Clientless SSL VPN (WebVPN) webvpn
enable
crypto ikev1 enable
IKEv1 VPN (Remote Access and crypto ikev1 policy
LAN-to-LAN) authentication rsa-sig
using Certificate-based Authentication tunnel-group ipsec-attributes
trust-point
crypto ikev2 enable
IKEv2 VPN (Remote Access and tunnel-group ipsec-attributes
LAN-to-LAN) ikev2 remote-authentication
using Certificate-based Authentication certificate
ikev2 local-authentication
certificate
Local Certificate Authority (CA) crypto ca server
no shutdown
Mobile Device Manager (MDM) Proxy mdm-proxy
enable
webvpn
mus password
Mobile User Security (MUS) mus server enable port
mus
Proxy Bypass webvpn
proxy-bypass
REST API ^1 rest-api image disk0:/
rest-api agent
SSH Access ^2,3 ssh
1. ASDM, CSM, and REST API services are accessible only from an IP address
in the configured http command range.
2. SSH service is accessible only from an IP address in the configured ssh
command range.
3. There is no workaround that addresses this vulnerability for SSH access.
FTD Software
In the following table, the left column lists the most common Cisco FTD
features that are potentially vulnerable. The right column indicates the
basic configuration for the feature from the show running-config CLI
command, if it can be determined.
Cisco FTD Feature Possible Vulnerable Configuration
AnyConnect SSL VPN ^1,2 webvpn
enable
Clientless SSL VPN (WebVPN) ^2 webvpn
enable
HTTP Service enabled ^3,4 http server enable
http
IKEv1 VPN (Remote Access and crypto ikev1 enable
LAN-to-LAN) crypto ikev1 policy
using Certificate-based Authentication authentication rsa-sig
^1,2 tunnel-group ipsec-attributes
trust-point
crypto ikev2 enable
IKEv2 VPN (Remote Access and tunnel-group ipsec-attributes
LAN-to-LAN) ikev2 remote-authentication
using Certificate-based Authentication certificate
^1,2 ikev2 local-authentication
certificate
SSH Service ^5,6 ssh
1. Remote Access VPN features are enabled by choosing Devices > VPN >
Remote Access in the Cisco FMC or Device > Remote Access VPN in Cisco
Firepower Device Manager (FDM).
2. The Clientless SSL VPN feature is not officially supported but can be
enabled through FlexConfig.
3. The HTTP feature is enabled by choosing Firepower Threat Defense
Platform Settings > HTTP in the Cisco Firepower Management Console (FMC).
4. HTTP service is accessible only from an IP address in the configured
http command range.
5. SSH is accessible only from an IP address in the configured ssh command
range.
6. There is no workaround that addresses this vulnerability for SSH access.
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 ASA
Software or FTD Software running on the following platforms:
3000 Series Industrial Security Appliances (ISAs)
ASA 5525-X, 5545-X, 5555-X, and 5585-X Security Appliances
ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco
7600 Series Routers
Adaptive Security Virtual Appliances (ASAv)
Firepower 2100 Series
Firepower 4100 Series
Firepower 9300 Series
Firepower Threat Defense Virtual (FTDv/NGFWv)
Secure Firewall 3100 Series
Workarounds
o There is a workaround that addresses this vulnerability for cryptographic
keys that are used with SSL/TLS features only. Cryptographic keys for use
with SSH cannot be imported to the device, so there is no workaround for
SSH.
To avoid the use of potentially weak cryptographic keys, administrators can
generate a key pair and a corresponding certificate on a trusted device
outside of the Cisco ASA or Cisco FTD device and then import the base 64
encoded PKCS #12 file that contains the keys and certificate(s) to the
Cisco ASA or Cisco FTD device using the crypto ca import pkcs12 command in
global configuration mode.
For more details, including steps for how to accomplish this task using the
Cisco Adaptive Security Device Manager (ASDM), see ASA 8.x: Renew and
Install the SSL Certificate with ASDM .
While this workaround has been deployed and was proven successful in a test
environment, customers should determine the applicability and effectiveness
in their own environment and under their own use conditions. Customers
should be aware that any workaround or mitigation that is implemented may
negatively impact the functionality or performance of their network based
on intrinsic customer deployment scenarios and limitations. Customers
should not deploy any workarounds or mitigations before first evaluating
the applicability to their own environment and any impact to such
environment.
Fixed Software
o 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.
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 .
Note: After upgrading to a fixed release, administrators must regenerate
all ECDSA and RSA key pairs that were generated on an affected device while
running a vulnerable release.
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 Cisco would like to thank ANSSI/CERT-FR, the French national and
governmental CSIRT, 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.
Subscribe to Cisco Security Notifications
o Subscribe
Related to This Advisory
o
URL
o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa5500x-entropy-6v9bHVYP
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2023-MAR-22 |
+----------+---------------------------+----------+--------+--------------+
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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