cisco-sa-asaftd-vpn-dos-SpOFF2ReHighCVSS 8.6

Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software VPN Web Server Denial of Service Vulnerability

Published
March 4, 2026
Last Modified
March 4, 2026

🔗 CVE IDs covered (1)

CVE-2026-20039 →

📋 Description

A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

This vulnerability is due to ineffective memory management of the VPN web server. An attacker could exploit this vulnerability by sending a large number of crafted HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

Cisco has released software updates that address this vulnerability. There are no 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-2026-20039 — Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability (CVSS 3.1 8.6, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H)

🎯 Affected products224

  • Cisco 3000 Series Industrial Security Appliances (ISA)
  • Cisco ASA 5500-X Series Firewalls
  • Cisco Adaptive Security Virtual Appliance (ASAv)
  • 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 Adaptive Security Appliance (ASA) Software
  • Cisco Secure Firewall Threat Defense (FTD) Software
  • Cisco Secure Firewall Threat Defense Virtual
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.1
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.1.2
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.1.3
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2.1
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2.4
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2.5
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2.9
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3.12
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3.2
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3.7
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3.9
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.4
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.4.10
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.4.13
  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.4.18
  • +194 more not shown

✅ Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com Workarounds: There are no workarounds that address this vulnerability.

🔗 References (7)