Cisco Security Advisory
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:X/RL:X/RC:X
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A vulnerability in the TLS handler of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software for Cisco Firepower 1000 Series firewalls could allow an unauthenticated, remote attacker to gain access to sensitive information.
The vulnerability is due to improper implementation of countermeasures against the Bleichenbacher attack for cipher suites that rely on RSA for key exchange. An attacker could exploit this vulnerability by sending crafted TLS messages to the device, which would act as an oracle and allow the attacker to carry out a chosen-ciphertext attack. A successful exploit could allow the attacker to perform cryptanalytic operations that may allow decryption of previously captured TLS sessions to the affected device.
To exploit this vulnerability, an attacker must be able to perform both of the following actions:
- Capture TLS traffic that is in transit between clients and the affected device
- Actively establish a considerable number of TLS connections to the affected device
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-asaftd-tls-bb-2g9uWkP
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Vulnerable Products
At the time of publication, this vulnerability affected Cisco Firepower 1000 Series firewalls if they were running a vulnerable release of Cisco ASA Software or FTD Software and had a feature enabled that caused the device to process TLS messages. These features include, but are not limited to, the following:
- AnyConnect SSL VPN
- Clientless SSL VPN
For information about which Cisco software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
Determine Whether a Device Could Process SSL or TLS Messages
To determine whether a device that is running Cisco ASA Software or FTD Software could process SSL or TLS packets, use the show asp table socket | include SSL|DTLS command and verify that it returns output. If this command returns any output, the device is vulnerable. If this command returns empty output, the device is not affected by the vulnerability described in this advisory. The following example shows the output of the show asp table socket | include SSL|DTLS command from a device that is vulnerable:
ftd# show asp table socket | include SSL|DTLS
SSL 0005aa68 LISTEN x.x.x.x:443 0.0.0.0:*
SSL 002d9e38 LISTEN x.x.x.x:8443 0.0.0.0:*
DTLS 0018f7a8 LISTEN 10.0.0.250:443 0.0.0.0:*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 Cisco products:
- ASA Software that is running on any platform other than Cisco Firepower 1000 Series
- FTD Software that is running on any platform other than Cisco Firepower 1000 Series
- Firepower Management Center (FMC) Software
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There are no workarounds that address this vulnerability. However, disabling use of TLS ciphers that rely on RSA for key exchange is a possible mitigation.
Cisco ASA Software
To specify the TLS ciphers to be used on a device that is running Cisco ASA Software, use the ssl cipher version custom command in global configuration mode. Use a custom string to allow only cipher suites based on Diffie-Hellman key exchange (DHE). Use the show ssl ciphers all command to view the list of supported ciphers for each TLS version.
Cisco FTD Software
On devices that are running Cisco FTD Software and are managed through Cisco FMC Software, TLS ciphers can be specified through Cisco FMC Software under Devices > Platform Settings > [Edit | New Policy] > SSL > [Edit | Add]. Then select a Custom security level and add the desired ciphers.
Cisco Firepower Device Manager (FDM) does not currently support the selection of specific SSL/TLS ciphers or cipher suites.
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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.
Fixed Releases
At the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
The left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerability described in this advisory and which release included the fix for this vulnerability.
Cisco ASA Software
Cisco ASA Software Release First Fixed Release for This Vulnerability Earlier than 9.131 Not applicable 9.13 9.13.1.13 9.14 9.14.1.30 1. Cisco ASA Software releases earlier than 9.13 do not support Cisco Firepower 1000 Series firewalls.Cisco FTD Software
Cisco FTD Software Release First Fixed Release for This Vulnerability Earlier than 6.4.01 Not applicable 6.4.0 6.4.0.10 6.5.0 6.5.0.5 (future release) 6.6.0 6.6.1 1. Cisco FTD Software releases earlier than 6.4.0 do not support Cisco Firepower 1000 Series firewalls.To upgrade to a fixed release of Cisco FTD Software, do one of the following:
- For devices that are managed by using Cisco Firepower Management Center (FMC), use the FMC interface to install the upgrade. After installation is complete, reapply the access control policy.
- For devices that are managed by using Cisco Firepower Device Manager (FDM), use the FDM interface to install the upgrade. After installation is complete, reapply the access control policy.
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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.
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This vulnerability was found during the resolution of a Cisco TAC support case.
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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.
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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2020-OCT-21
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