A vulnerability in the TLS 1.3 implementation of the Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the Snort 3 detection engine to unexpectedly restart. This vulnerability is due to a logic error in how memory allocations are handled during a TLS 1.3 session. Under specific, time-based constraints, an attacker could exploit this vulnerability by sending a crafted TLS 1.3 message sequence through an affected device. A successful exploit could allow the attacker to cause the Snort 3 detection engine to reload, resulting in a denial of service (DoS) condition. While the Snort detection engine reloads, packets going through the FTD device that are sent to the Snort detection engine will be dropped. The Snort detection engine will restart automatically. No manual intervention is required. Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort3-uAnUntcV 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.
A vulnerability in the TLS 1.3 implementation of the Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the Snort 3 detection engine to unexpectedly restart.
This vulnerability is due to a logic error in how memory allocations are handled during a TLS 1.3 session. Under specific, time-based constraints, an attacker could exploit this vulnerability by sending a crafted TLS 1.3 message sequence through an affected device. A successful exploit could allow the attacker to cause the Snort 3 detection engine to reload, resulting in a denial of service (DoS) condition. While the Snort detection engine reloads, packets going through the FTD device that are sent to the Snort detection engine will be dropped. The Snort detection engine will restart automatically. No manual intervention is required.
Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort3-uAnUntcV
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.
At the time of publication, this vulnerability affected devices that were running a vulnerable release of Cisco FTD Software and for which both of the following conditions were true:
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
To determine if Snort 3 is running on Cisco FTD Software, see Determine the Active Snort Version that Runs on Firepower Threat Defense (FTD). Snort 3 has to be active for this vulnerability to be exploited.
SSL decryption policies are not configured by default.
Determine Cisco FTD Software SSL Policy Configuration Using the FTD Software CLI
To determine whether an SSL policy is configured on a device that is running Cisco FTD Software, log in to the Cisco FTD Software CLI and use the show ssl-policy-config command.
If the command output shows SSL policy not yet applied, the device is not affected by this vulnerability, as shown in the following example:
>show ssl-policy-config
SSL policy not yet applied
If the command output shows a policy, the device has an SSL policy applied and could be affected by this vulnerability if TLS 1.3 decryption is enabled, as shown in the following example:
> show ssl-policy-config
===================[ CSCwc59953 ]===================
=================[ Default Action ]=================
Default Action : Do Not Decrypt
...
Determine Cisco FTD Software SSL Policy Configuration for Devices that Are Managed by Cisco Firepower Device Manager Software
To determine whether an SSL policy is configured on a device that is managed by Cisco Firepower Device Manager (FDM) Software, complete the following steps:
For detailed information about SSL decryption policies, see the SSL Decryption chapter of the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.
Determine Cisco FTD Software SSL Policy Configuration for Devices that Are Managed by Cisco Firepower Management Center Software
To determine whether an SSL policy is configured on a device that is managed by Cisco Firepower Management Center (FMC) Software, complete the following steps:
For detailed information about SSL decryption policies, see the SSL Policy chapter of the Cisco Secure Firewall Management Center Configuration Guide.
Determine Cisco FTD Software SSL Policy Configuration for Devices that Are Managed by Cisco Defense Orchestrator
To determine whether an SSL policy is configured on a device that is managed by Cisco Defense Orchestrator, complete the following steps:
For detailed information about Cisco Defense Orchestrator managed devices, see the Cisco Defense Orchestrator documentation.
For detailed information about SSL decryption policies for Cisco FMC Devices managed with Cisco Defense Orchestrator, see the Decryption Policies chapter of Managing Firewall Threat Defense with Cloud-delivered Firewall Management Center in Cisco Defense Orchestrator.
For detailed information about SSL decryption policies for Cisco FDM Devices managed with Cisco Defense Orchestrator, see the SSL Decryption Policy section of the Managing FDM Devices with Cisco Defense Orchestrator guide.
The default setting for TLS 1.3 decryption varies by platform when an SSL policy is configured. Note that TLS 1.3 decryption for Cisco FDM controlled devices is not offered until Cisco FTD Release 7.3.0. TLS 1.3 decryption is offered in Cisco FTD Release 7.2.0 for devices that are managed by Cisco FMC and Cisco Defense Orchestrator.
These are the default settings for the platforms:
Determine Cisco FTD Software TLS 1.3 Decryption Configuration Using the FTD Software CLI
To determine from the CLI whether TLS 1.3 decryption is configured on a device, log in to the Cisco FTD Software CLI and use the grep tls13 /ngfw/var/sf/detection_engines/*/ssl/ssl.rules command.
> expert
admin@ftd:~$
admin@ftd:~$grep tls13 /ngfw/var/sf/detection_engines/*/ssl/ssl.rules
"tls13_decryption" "true";
Determine Cisco FTD Software TLS 1.3 Decryption Configuration for Devices that Are Managed by Cisco FDM Software
To determine whether TLS 1.3 Decryption is configured on a device that is managed by Cisco FDM Software, complete the following steps:
For detailed information about TLS 1.3 decryption, see the Configure Advanced and Undecryptable Traffic Settings section in the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.
Determine Cisco FTD Software TLS 1.3 Decryption Configuration for Devices that Are Managed by Cisco FMC Software
To determine whether TLS 1.3 Decryption is configured on a device that is managed by Cisco FMC Software, complete the following steps:
For detailed information about TLS 1.3 decryption, see the SSL Policy Advanced Options section in the Cisco Secure Firewall Management Center Configuration Guide.
Determine Cisco FTD Software TLS 1.3 Decryption Configuration for Devices that Are Managed by Cisco Defense Orchestrator Software
To determine whether TLS 1.3 Decryption is configured on a device that is managed by Cisco Defense Orchestrator, complete the following steps:
For detailed information about devices that are managed by Cisco Defense Orchestrator, see the Cisco Defense Orchestrator documentation.
For detailed information about TLS 1.3 decryption, see the Decryption Policy Advanced Options section of Managing Firewall Threat Defense with Cloud-Delivered Firewall Management Center in Cisco Defense Orchestrator.
For detailed information about TLS 1.3 decryption for Cisco FDM Devices managed with Cisco Defense Orchestrator, see the SSL Decryption Policy section of Managing FDM Devices with Cisco Defense Orchestrator.
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 products:
There are workarounds and mitigations that address this vulnerability. To remove the attack vector for this vulnerability, either of the following two options can be used. Only one of the two options needs to be applied.
Before downgrading, review the Before you Begin section in the Switching Between Snort 2 and Snort 3 section in the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.
Note: Downgrading to Snort 2 will delete customer policies, NAP customizations, and Hostname redirect in active authentications. To discuss the effects of reverting on your deployment, contact the Technical Assistance Center (TAC).
Reverting to Snort 2 for Cisco FTD devices managed by FDM Software
To revert to Snort 2 on a device that is managed by Cisco FDM Software, complete the following steps:
After making the changes above, deploy changes to your Cisco FTD devices.
For detailed information about reverting to Snort 2, see the Switching Between Snort 2 and Snort 3 section in the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.
Reverting to Snort 2 for Cisco FTD devices managed by FMC Software
To revert to Snort 2 on a device that is managed by Cisco FMC Software, complete the following steps:
After making the changes above, deploy changes to your FTD devices.
For detailed information about reverting to Snort 2, see the Snort 3 Inspection Engine chapter of the Cisco Secure Firewall Management Center Snort 3 Configuration Guide.
Reverting to Snort 2 for Cisco FTD devices managed by Cisco Defense Orchestrator
To revert to Snort 2 on a device that is managed by Cisco Defense Orchestrator, complete the following steps:
After making the changes above, deploy changes to your Cisco FTD devices.
For detailed information about Cisco Defense Orchestrator managed devices, see the Cisco Defense Orchestrator documentation.
For detailed information about reverting to Snort 2 for Cisco FMC Devices managed with Cisco Defense Orchestrator, see the Snort 3 Inspection Engine chapter of the Cisco Secure Firewall Management Center Snort 3 Configuration Guide.
For detailed information about reverting to Snort 2 for Cisco FDM Devices managed with Cisco Defense Orchestrator, see the Revert From Snort 3.0 for FDM-Managed Device section of the Managing FDM Devices with Cisco Defense Orchestrator guide.
This mitigation can affect your client and server connections. When TLS 1.3 decryption is disabled, the TLS connection downgrades to TLS 1.2 while matching the decryption rule. The effects on the deployment will depend on the clients and servers that will connect through the Cisco FTD device. To discuss the effects this will have on your deployment, contact the Technical Assistance Center (TAC) .
Disabling TLS 1.3 for Cisco FTD Software devices managed by FDM Software
To disable TLS 1.3 Decryption on a device that is managed by Cisco FDM Software, complete the following steps:
After changing the policy above, deploy the new policy to your Cisco FTD devices.
For detailed information about TLS 1.3 decryption, see the Configure Advanced and Undecryptable Traffic Settings section in the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.
Disabling TLS 1.3 for Cisco FTD Software devices managed by FMC Software
To disable TLS 1.3 Decryption on a device that is managed by Cisco FMC Software, complete the following steps:
After changing the policy above, deploy the new policy to your FTD devices.
For detailed information about TLS 1.3 decryption, see the SSL Policy Advanced Options section in the Cisco Secure Firewall Management Center Configuration Guide.
Disabling TLS 1.3 for Cisco FTD Software devices managed by Cisco Defense Orchestrator
To disable TLS 1.3 Decryption on a device that is managed by Cisco Defense Orchestrator, complete the following steps:
After changing the policy above, deploy the new policy to your FTD devices.
For detailed information about devices managed by Cisco Defense Orchestrator, see the Cisco Defense Orchestrator documentation.
For detailed information about TLS 1.3 decryption, see the Decryption Policy Advanced Options section of Managing Firewall Threat Defense with Cloud-Delivered Firewall Management Center in Cisco Defense Orchestrator.
For detailed information about TLS 1.3 decryption for Cisco FDM Devices managed with Cisco Defense Orchestrator, see the SSL Decryption Policy section of Managing FDM Devices with Cisco Defense Orchestrator.
While these workarounds and mitigations have been deployed and were 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.
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.
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:
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
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.
This vulnerability was found during the resolution of a Cisco TAC support case.
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 | 2023-NOV-01 |
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