Cisco Patches Actively Exploited ASA and FTD VPN Flaw That Can Crash Firewalls

Cisco has released patches to address a high-severity security flaw in Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software that it said has been exploited in the wild.

The vulnerability, tracked as CVE-2026-76418 , is rated 8.6 on the CVSS scoring system. Successful exploitation could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial-of-service (DoS) condition.

According to Cisco, the issue is rooted in the Remote Access SSL VPN service of ASA and FTD software.

"This vulnerability is due to logic errors when secondary authentication is configured on a tunnel group," it said in a Wednesday advisory. "An attacker could exploit this vulnerability by sending a crafted request when connecting to the SSL remote access VPN. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition."

The network equipment major said it became aware of active exploitation of this vulnerability in October 2026, but did not any specifics as to when the attacks began, who is behind them, and the scale of the efforts.

Fixes for the flaw are available in the following versions -

Cisco Secure Firewall ASA Software Release 9.16 and earlier - Fixed in 9.16.4.104 9.18 - Fixed in 9.18.4.96 9.20 - Fixed in 9.20.4.50 9.22 - Fixed in 9.22.3.200 9.23 - Fixed in 9.23.1.48 9.24 - Fixed in 9.24.1.27 and 9.24.10.1

9.16 and earlier - Fixed in 9.16.4.104

9.18 - Fixed in 9.18.4.96

9.20 - Fixed in 9.20.4.50

9.22 - Fixed in 9.22.3.200

9.23 - Fixed in 9.23.1.48

9.24 - Fixed in 9.24.1.27 and 9.24.10.1

Cisco Secure FTD Software Release 7.0 and earlier - Fixed in 7.0.11 7.2 - Fixed in 7.2.13 7.4 - Fixed in 7.4.9 7.6 - Fixed in 7.6.7 7.7 - Fixed in 7.7.14 10.0 - Fixed in 10.0.3 10.1 - Fixed in 10.1.1

7.0 and earlier - Fixed in 7.0.11

7.2 - Fixed in 7.2.13

7.7 - Fixed in 7.7.14

10.0 - Fixed in 10.0.3

10.1 - Fixed in 10.1.1

Cisco also noted that the vulnerability affects Cisco devices if the following conditions are met -

They are running a vulnerable release of Cisco Secure Firewall ASA Software or Cisco Secure FTD Software.

The SSL remote access VPN login service is reachable.

Secondary authentication is configured in the tunnel group scope.

"If tunnel-group-list enable is configured, check all tunnel groups, including the default tunnel group, DefaultWEBVPNGroup, for secondary-authentication-server-group," Cisco said.

"If tunnel-group-list enable is absent or has been removed using the no tunnel-group-list enable command, check the default tunnel group, DefaultWEBVPNGroup, for secondary-authentication-server-group because disabling the group list does not remove exposure when that default group uses secondary authentication."

As a temporary mitigation, the company is recommending that customers turn off the tunnel group list if DefaultWEBVPNGroup does not use secondary authentication, or disable secondary authentication on any user-configured tunnel group list or on the default tunnel group, DefaultWEBVPNGroup.

"On Cisco Secure FTD Software, review the deployed remote access VPN policy and the resulting device running configuration in Cisco Secure FMC Software or Cisco Secure FDM," Cisco said. "A successful VPN login is not required to reach the affected processing path."

The disclosure comes as Cisco revealed that a sophisticated advanced persistent threat (APT) actor tracked as UAT-11473 weaponized CVE-2026-20127 , an authentication bypass vulnerability in Cisco SD-WAN Catalyst Controller instances, to bypass authentication and gain unauthorized access to affected systems.

The activity, which has targeted space and satellite services, defense and aerospace technology, and policy research sectors, is assessed to infrastructure overlaps with Volt Typhoon's Silent Train covert network.

"UAT-11473 then installed a custom malware framework we track as 'KeyDrift' consisting of multiple components [like PolyFlame and LittleFilch] geared towards collecting sensitive keying information, acting as backdoors and intermediate command-and-control (C2) hosts," Cisco Talos said .

"The framework is designed to provide long-term persistent access and automated exfiltration of sensitive keying material. KeyDrift operates inside SD-WAN control-plane processes and is capable of intercepting decrypted control traffic, extracting control-session metadata and data-plane keying material, and staging or transmitting the collected material using encrypted records."