cisco-sa-ftd-tcp-dos-rHfqnwRgMediumCVSS 5.8

Cisco Secure Firewall Threat Defense Software TLS with Snort 3 Detection Engine Denial of Service Vulnerability

Published
March 4, 2026
Last Modified
March 4, 2026

🔗 CVE IDs covered (1)

CVE-2026-20006 →

📋 Description

A vulnerability in the TLS cryptography functionality of the Snort 3 Detection Engine of Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to unexpectedly restart, resulting in a denial of service (DoS) condition.

This vulnerability is due to improper implementation of the TLS protocol. An attacker could exploit this vulnerability by sending a crafted TLS packet to an affected system. A successful exploit could allow the attacker to cause a device that is running Cisco Secure FTD Software to drop network traffic, resulting in a DoS condition.

Note: TLS 1.3 is not affected by this vulnerability.

Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.

This advisory is part of the March 2026 release of the Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication ["https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-75736"].

CVE-2026-20006 — Cisco Firepower Threat Defense Software and Cisco FirePOWER Services TLS with Snort 3 Denial of Service Vulnerability (CVSS 3.1 5.8, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L)

🎯 Affected products43

  • Cisco 3000 Series Industrial Security Appliances (ISA)
  • Cisco Firepower 1000 Series
  • Cisco Firepower 2100 Series
  • Cisco Firepower 4100 Series
  • Cisco Firepower 9000 Series
  • Cisco Secure Firewall 1200 Series
  • Cisco Secure Firewall 3100 Series
  • Cisco Secure Firewall 4200 Series
  • Cisco Secure Firewall Threat Defense (FTD) Software
  • Cisco Secure Firewall Threat Defense Virtual
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.0
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.0.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.10
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.10.2
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.2
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.3
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.4
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.4.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.5
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.5.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.5.2
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.6
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.7
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.8
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.8.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.2.9
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.3.0
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.3.1
  • Cisco Secure Firewall Threat Defense (FTD) Software 7.3.1.1
  • +13 more not shown

✅ Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com Workaround: As a workaround for this vulnerability, configure the device so that traffic from a specific TLS version is not blocked. To implement the workaround, complete the following steps: Log in to the Cisco Secure FMC Software web-based management interface. From the Policies menu, choose Access Control > SSL or Access Control > Decryption. Choose the appropriate SSL or decryption policy. Click the Edit pencil icon. Choose the appropriate rule. Click the Edit pencil icon. Click the Version tab. Ensure that all version check boxes are checked. Click Save to deploy the changes. 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. Workarounds: As a workaround for this vulnerability, configure the device so that traffic from a specific TLS version is not blocked. To implement the workaround, complete the following steps: Log in to the Cisco Secure FMC Software web-based management interface. From the Policies menu, choose Access Control > SSL or Access Control > Decryption. Choose the appropriate SSL or decryption policy. Click the Edit pencil icon. Choose the appropriate rule. Click the Edit pencil icon. Click the Version tab. Ensure that all version check boxes are checked. Click Save to deploy the changes. 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.

🔗 References (6)