Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software for Secure Firewall 3100 and 4200 Series DTLS Denial of Service Vulnerability

There is a workaround that addresses this vulnerability. Use the no flow-offload-dtls CLI command to disable DTLS flow offload.

Note: For devices that are running Cisco FTD Software, the no flow-offload-dtls command can be pushed using FlexConfig.

Disabling DTLS flow offload will cause DTLS-encrypted traffic to be processed in software rather than hardware, which may reduce throughput and increase CPU utilization on the affected device. This impact will be more significant in deployments with a high volume of DTLS sessions.

While this workaround has been deployed and was 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.

Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.

Fixed Releases

In the following table, the left column lists Cisco software releases. The center column lists hot fixes that are affected by the vulnerabilities that are described in this advisory, and the right column indicates the first software release that includes the fix for these vulnerabilities. Customers who installed one of the listed hot fix releases must install the listed first fixed release.

In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities.

Cisco strongly recommends that customers upgrade to the first fixed releases in the preceding tables because they include fixes for multiple vulnerabilities. For more information, see Cisco Secure Firewall Adaptive Security Appliance, Secure Firewall Threat Defense, and Secure Firewall Management Center Software Hardening Release: September 2026.

Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software

To help customers determine their exposure to vulnerabilities in Cisco Secure Firewall ASA, Secure FMC, and Secure 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, 9.20.3.4 for Cisco Secure Firewall ASA Software or 7.4.2 for Cisco Secure FTD Software.

5. Click Check.

Additional Resources

For help determining the best Cisco Secure Firewall ASA, Secure FMC, or Secure FTD Software release, see the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

Cisco Secure Firewall ASA Compatibility

Cisco Secure Firewall ASA Upgrade Guide

Cisco Secure Firewall Threat Defense Compatibility Guide