Cisco Firepower Threat Defense Software SSL and Snort 3 Detection Engine Bypass and Denial of Service Vulnerability
cisco-sa-ftd-snort3-8U4HHxH8 · Medium · Published · Updated
A vulnerability in the SSL/TLS certificate handling of Snort 3 Detection Engine integration with Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the Snort 3 detection engine to restart. This vulnerability is due to a logic error that occurs when an SSL/TLS certificate that is under load is accessed when it is initiating an SSL connection. Under specific, time-based constraints, an attacker could exploit this vulnerability by sending a high rate of SSL/TLS connection requests to be inspected by the Snort 3 detection engine on an affected device. A successful exploit could allow the attacker to cause the Snort 3 detection engine to reload, resulting in either a bypass or a denial of service (DoS) condition, depending on device configuration. See the Details section of this advisory for more information. 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-snort3-8U4HHxH8 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 is a workaround and mitigations that address this vulnerability. To remove the attack vector for this vulnerability, either revert to Snort 2, or, if remaining on Snort 3, disable both TLS server identity discovery and any configured decryption policy. If either is enabled, the device is still vulnerable.
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 by Using the CLI
There is no option to revert to snort 2 by using the CLI.
Reverting to Snort 2 for Cisco FTD Devices that Are 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 FTD devices.
Reverting to Snort 2 for Cisco FTD Devices that Are 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 that Are 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 FTD devices.
To disable the TLS server identity discovery for devices managed by Cisco FDM Software, do the following:
Log in to the Cisco FDM web interface.
From the Policies menu, choose Access Control.
Click on the Settings gear icon.
If the TLS Server Identity Discovery setting is enabled, disable it and click OK.
To disable the SSL Policy for devices managed by Cisco FDM Software, do the following:
Log in to the Cisco FDM web interface.
From the Policies menu, choose SSL Decryption.
If a policy name is present, disable SSL Decryption.
After changing the policies above, deploy the new policies to your Cisco FTD devices.
Mitigation for Devices that Are Managed by Cisco FMC Software
Both the TLS server identity discovery and SSL policy must be disabled to implement the workaround. Disabling only one item will leave the device vulnerable.
To navigate to the correct configuration page to disable the policies for devices that are managed by Cisco FMC Software, do the following:
Log in to the Cisco FMC web interface.
From the Policies menu, choose Access Control.
Choose the appropriate Access Control Policy.
Click the Edit pencil icon.
Click on the Advanced tab.
To disable the TLS server identity discovery for devices that are managed by Cisco FMC Software, do the following:
Locate the TLS Server Identity Discovery setting.
If the setting is enabled, click the Edit pencil icon.
Uncheck the Early application detection and URL categorization box and choose OK.
Click Save to save the policy.
To disable the SSL Policy for devices that are managed by Cisco FMC Software, do the following:
Locate the SSL Policy Settings.
If a policy name is present, click the Edit pencil icon.
In the Drop-down menu, choose None and then OK
Click Save to save the policy.
After changing the policies above, deploy the new policies to your Cisco FTD devices.
To navigate to the correct configuration page to disable the policies for devices that are managed by Cisco Defense Orchestrator Software, do the following:
Log in to the Cisco Defense Orchestrator web interface.
From the CDO Policies menu, choose FTD Policies.
From the FTD Policies menu, choose Access Control.
Choose the appropriate Access Control Policy.
Click the Edit pencil icon.
Choose More and then Click on then Advanced Settings
To disable the TLS server identity discovery for devices that are managed by Cisco Defense Orchestrator software, do the following:
Locate the TLS Server Identity Discovery setting.
If the setting is enabled, click the Edit pencil icon.
Uncheck the Early application detection and URL categorization box and choose OK.
Click Save to save the policy
To disable the SSL Policy for devices that are managed by Cisco Defense Orchestrator software, do the following:
Locate the Decryption Policy Settings.
If a policy name is present, click the Edit pencil icon
In the Drop-down menu, choose None and then OK.
Click Save to save the policy
After changing the policies above, deploy the new policies to your Cisco Defense Orchestrator 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.