Cisco Firepower Threat Defense Software Snort 3 Detection Engine Denial of Service Vulnerability
cisco-sa-ftd-snort3-uAnUntcV · Medium · Published · Updated
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.
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.
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) https://www.cisco.com/go/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:
Log in to the Cisco FTD Software web interface.
From the main menu, choose Device.
In the Updates area, choose View Configuration.
In the Intrusion Rule section, choose Downgrade to 2.0.
After making the changes above, deploy changes to your Cisco FTD devices.
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:
Log in to the Cisco FMC Software web interface.
From the Devices menu, choose Device Management.
Choose the appropriate Cisco FTD device.
Click the Edit pencil icon.
Choose the Device tab.
In the Inspection Engine area, choose Revert to Snort 2.
After making the changes above, deploy changes to your FTD devices.
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:
Log in to the Cisco Defense Orchestrator web interface.
In the navigation bar, click Inventory.
Click the Devices tab.
Click the FTD tab and click the device you want to revert.
In the Device Actions pane located to the right, click Upgrade.
Set the upgrade toggle to Intrusion Prevention Engine.
Click Revert to Snort Engine 2.0.
After making the changes above, deploy changes to your Cisco FTD devices.
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:
Log in to the Cisco FTD Software web interface.
From the main menu, choose Policies.
Choose the SSL Decryption tab.
Click the SSL Decryption Settings button.
Click on the Advanced tab.
Disable the TLS 1.3 Decryption setting.
Click OK.
After changing the policy above, deploy the new policy to your Cisco FTD devices.
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:
Log in to the Cisco FMC Software web interface.
From the Policies menu, choose SSL.
Choose the appropriate SSL Policy.
Click the Edit pencil icon.
Click the Advanced Settings tab.
Uncheck the Enable TLS 1.3 Decryption box.
Click Save to save your changes.
After changing the policy above, deploy the new policy to your FTD devices.
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:
Log in to the Cisco Defense Orchestrator web interface.
From the Cisco Defense Orchestrator Policies menu, choose FTD Policies.
From the FTD Policies menu, choose Decryption.
Choose the appropriate Decryption Policy.
Click the Edit pencil icon.
Click the Advanced Settings tab.
Disable Enable TLS 1.3 Decryption.
Click Save.
After changing the policy above, deploy the new policy to your FTD devices.
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.