Summary

• 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.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco FTD Software if it was running a vulnerable release and met all of the following conditions:

  • The device was running Snort 3.
  • At least one of the following conditions was true:
    • TLS server identity discovery was enabled.
    • An SSL policy was configured.

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. 

  Determine Cisco FTD Software Snort Configuration

  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.

  Determine Cisco FTD Software TLS Server Identity Discovery Configuration

  TLS server identity discovery is disabled by default.

  Determine Cisco FTD Software TLS Server Identity Discovery Configuration Using the FTD Software CLI

  To determine whether TLS server identity discovery is configured on a device that is running Cisco FTD Software, log in to the Cisco FTD Software CLI and use the show access-control-config command. Scroll down to the Advanced Settings section. If the command output shows TLS Server Identity Discovery Enabled, the device is affected by this vulnerability, as shown in the following example: 

  > show  access-control-config
  ===============[ Advanced Settings ]================
  General Settings
    Maximum URL Length                  : 1024
    Interactive Block Bypass Timeout    : 600
    SSL Policy                          : Certificate-Visibility-SSL-Policy
    TLS Server Identity Discovery       : Enabled
  

  The following example shows that TLS server identity discovery is disabled:

  >show access-control-config
  ===============[ Advanced Settings ]================
  General Settings
    Maximum URL Length                  : 1024
    Interactive Block Bypass Timeout    : 600
    TLS Server Identity Discovery       : Disabled
  

  Note: Due to CSCvz06256, this command will not show the TLS server identity discovery setting for the Cisco FTD 7.0 software train.

  Determine Cisco FTD Software TLS Server Identity Discovery Configuration for Devices Managed by Cisco Firepower Device Manager Software

  To determine whether TLS server identity discovery is configured on a device that is managed by Cisco Firepower Device Manager (FDM) Software, complete the following steps:

  1. Log in to the Cisco FDM web interface.
  2. From the Policies menu, choose Access Control.
  3. Click on the Settings gear icon.
  4. Locate the TLS Server Identity Discovery setting.
     • If the setting is enabled, the device is affected by this vulnerability.
     • If the setting is disabled, the device might not be affected by this vulnerability.

  For detailed information about TLS server identity discovery, see the Access Control chapter of the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.

  Determine Cisco FTD Software TLS Server Identity Discovery Configuration for Devices Managed by Cisco Firepower Management Center Software

  To determine whether TLS server identity discovery is configured on a device that is managed by Cisco Firepower Management Center (FMC) Software, complete the following steps:

  1. Log in to the Cisco FMC web interface.
  2. From the Policies menu, choose Access Control.
  3. Choose the appropriate Access Control Policy.
  4. Click the Edit pencil icon.
  5. Click on the Advanced tab.
  6. Locate the TLS Server Identity Discovery setting.
     • If the setting is enabled, the device is affected by this vulnerability.
     • If the setting is disabled, the device might not be affected by this vulnerability.

  For detailed information about TLS server identity discovery, see the Access Control Policy chapter of the Cisco Secure Firewall Management Center Device Configuration Guide.

  Determine Cisco FTD Software TLS Server Identity Discovery Configuration for Cisco Defense Orchestrator Devices

  To determine whether TLS server identity discovery is configured on a device that is managed by Cisco Defense Orchestrator Software, complete the following steps:

  1. Log in to the Cisco Defense Orchestrator web interface.
  2. From the Cisco Defense Orchestrator Policies menu, choose FTD Policies.
  3. From the FTD Policies menu, choose Access Control.
  4. Choose the appropriate Access Control Policy.
  5. Click the Edit pencil icon.
  6. Choose More and then Click on then Advanced Settings.
  7. Locate the TLS Server Identity Discovery setting.
     • If the setting is enabled, the device is affected by this vulnerability.
     • If the setting is disabled, the device might not be affected by this vulnerability.

  For detailed information about TLS server identity discovery, see the Cisco Defense Orchestrator documentation.

  Determine Cisco FTD Software SSL Policy Configuration

  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 a policy, the device has an SSL policy applied and is affected by this vulnerability, as shown in the following example: 

  > show ssl-policy-config
  ===================[ CSCwc07015 ]===================
  =================[ Default Action ]=================
  Default Action            : Do Not Decrypt
  ...

  In the following example, no SSL policy is applied:

  >show ssl-policy-config
  SSL policy not yet applied

  Determine Cisco FTD Software SSL Policy Configuration for Devices Managed by Cisco FDM

  To determine whether an SSL policy is configured on a device that is managed by Cisco FDM Software, complete the following steps:

  1. Log in to the Cisco FTD web interface.
  2. From the main menu, choose Policies.
  3. Choose the SSL Decryption tab.
  • If a Policy Name is listed, the device is affected by this vulnerability.
  • If SSL decryption is not enabled, the device might not affected by this vulnerability.

  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 Managed by Cisco FMC Software

  To determine whether an SSL policy is configured on a device that is managed by Cisco FMC Software, complete the following steps:

  1. Log in to the Cisco FMC web interface.
  2. From the Policies menu, choose Access Control.
  3. Choose the appropriate Access Control Policy.
  4. Click the Edit pencil icon.
  5. Look in the SSL Policy area.
     
     • If a Policy Name is listed, the device is affected by this vulnerability.
     • If None is listed, the device might not affected by this vulnerability.

  For detailed information about SSL decryption policies, see the SSL Policy chapter of the Cisco Secure Firewall Management Center Device Configuration Guide.

  Determine Cisco FTD Software SSL Policy Configuration for Devices 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:

  1. Log in to the Cisco Defense Orchestrator web interface.
  2. From the Cisco Defense Orchestrator Policies menu, choose the FTD Policies.
  3. From the FTD Policies menu, choose Access Control.
  4. Choose the appropriate Access Control Policy.
  5. Click the Edit pencil icon.
  6. Look in the Decryption Policy area.
  • If a Policy Name is listed, the device is affected by this vulnerability.
  • If None is listed, the device is not affected by this vulnerability.

  For detailed information about devices managed by Cisco Defense Orchestrator, see the Cisco Defense Orchestrator documentation.

  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 products:

  • Cisco Adaptive Security Appliance (ASA) Software
  • Cisco FMC Software
  • Open Source Snort 2
  • Open Source Snort 3

Details

• The following Cisco FTD Software Snort 3 configuration parameters govern how traffic is handled if the Snort 3 process restarts, which could change how encrypted traffic is handled during an exploit of this vulnerability.

  • Snort Fail Open
  • Snort preserve-connection

  For additional information, see the Snort Restart Traffic Behavior section of the Firepower Management Center Configuration Guide or the  Managing Firewall Threat Defense with Cloud-delivered Firewall Management Center in Cisco Defense Orchestrator guide.

Workarounds

• 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: For TLS server identity discovery to be enabled, a decryption policy does not need to be configured and associated with the access control policy.

  Reverting to Snort 2

  Before reverting to Snort 2, 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 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:

  1. Log in to the Cisco FTD Software web interface.
  2. From the main menu, choose Device.
  3. In the Updates area, choose View Configuration.
  4. In the Intrusion Rule section, choose Downgrade to 2.0.

  After making the changes above, deploy changes to your 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 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:

  1. Log in to the Cisco FMC Software web interface.
  2. From the Devices menu, choose Device Management.
  3. Choose the appropriate Cisco FTD device.
  4. Click the Edit pencil icon.
  5. Choose the Device tab.
  6. In the Inspection Engine area, choose Revert to Snort 2.

  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 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:

  1. Log in to the Cisco Defense Orchestrator web interface.
  2. In the navigation bar, click Inventory.
  3. Click the Devices tab.
  4. Click the FTD tab and click the device you want to revert.
  5. In the Device Actions pane located to the right, click Upgrade. 
  6. Set the upgrade toggle to Intrusion Prevention Engine.
  7. Click Revert to Snort Engine 2.0.

  After making the changes above, deploy changes to your FTD devices.

  For detailed information about devices managed by Cisco Defense Orchestrator, 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 Managing FDM Devices with Cisco Defense Orchestrator. 

  Mitigation for Devices that Are Managed by Cisco FDM Software

  For Cisco FTD devices that stay on Snort 3, 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 disable the TLS server identity discovery for devices managed by Cisco FDM Software, do the following:

  1. Log in to the Cisco FDM web interface.
  2. From the Policies menu, choose Access Control.
  3. Click on the Settings gear icon.
  4. 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:

  1. Log in to the Cisco FDM web interface.
  2. From the Policies menu, choose SSL Decryption.
  3. If a policy name is present, disable SSL Decryption.

  After changing the policies above, deploy the new policies to your Cisco FTD devices.

  For more information, see the Access Control Chapter of the Cisco Firepower Threat Defense Configuration Guide for Firepower Device Manager.

  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:

  1. Log in to the Cisco FMC web interface.
  2. From the Policies menu, choose Access Control.
  3. Choose the appropriate Access Control Policy.
  4. Click the Edit pencil icon.
  5. Click on the Advanced tab.

  To disable the TLS server identity discovery for devices that are managed by Cisco FMC Software, do the following:

  1. Locate the TLS Server Identity Discovery setting.
  2. If the setting is enabled, click the Edit pencil icon.
  3. Uncheck the Early application detection and URL categorization box and choose OK.
  4. Click Save to save the policy.

  To disable the SSL Policy for devices that are managed by Cisco FMC Software, do the following:

  1. Locate the SSL Policy Settings.
  2. If a policy name is present, click the Edit pencil icon.
  3. In the Drop-down menu, choose None and then OK
  4. Click Save to save the policy.

  After changing the policies above, deploy the new policies to your Cisco FTD devices.

  For more information, see the Access Control Chapter  of the Firepower Management Center Device Configuration Guide.

  Mitigation for Devices that Are Managed by Cisco Defense Orchestrator

  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 Defense Orchestrator Software, do the following:

  1. Log in to the Cisco Defense Orchestrator web interface.
  2. From the CDO Policies menu, choose FTD Policies.
  3. From the FTD Policies menu, choose Access Control.
  4. Choose the appropriate Access Control Policy.
  5. Click the Edit pencil icon.
  6. 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:

  1. Locate the TLS Server Identity Discovery setting.
  2. If the setting is enabled, click the Edit pencil icon.
  3. Uncheck the Early application detection and URL categorization box and choose OK.
  4. Click Save to save the policy

  To disable the SSL Policy for devices that are managed by Cisco Defense Orchestrator software, do the following:

  1. Locate the Decryption Policy Settings.
  2. If a policy name is present, click the Edit pencil icon
  3. In the Drop-down menu, choose None and then OK.
  4. Click Save to save the policy

  After changing the policies above, deploy the new policies to your Cisco Defense Orchestrator devices.

  For more information, see the Cisco Defense Orchestrator documentation.

  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.

Fixed Software

• 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

  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.

  Only this advisoryAll Critical and High advisoriesAll advisoriesCisco ASA SoftwareCisco FMC SoftwareCisco FTD SoftwareAny Platform3000 Series Industrial Security Appliances (ISA)ASA 5500-X Series FirewallsASA Service ModuleAdaptive Security Virtual Appliance (ASAv)Firepower 1000 SeriesFirepower 2100 SeriesFirepower 4100 SeriesFirepower 9000 SeriesSecure Firewall 3100 Series

   

   

  For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide.

   

  Additional Resources

  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

Exploitation and Public Announcements

• 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

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort3-8U4HHxH8

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2023-NOV-01

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