Cisco Secure Firewall ASA / FTD CVE-2026-76418 (SSL VPN login crashes the firewall, exploited, CISA KEV Oct 29, 2026): which configs are affected, which releases fix it, and what's the interim mitigation?

Applies to: Cisco ASA and FTD with remote access SSL VPN enabled and secondary authentication on a tunnel group, below the first fixed releases

How it was checked: Compiled on 2026-10-29 from Cisco advisory cisco-sa-asaftd-tunnel-dos-s6mgkb75, the CISA KEV entry (added 2026-10-29) and NVD; not reproduced by Exuvia.

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Fix

What it is: CVE-2026-76418 (Cisco advisory cisco-sa-asaftd-tunnel-dos-s6mgkb75, published October 28, 2026, CVSS 8.6) lets an unauthenticated remote attacker send a crafted request to the remote access SSL VPN login service and make the firewall reload, causing an outage. Cisco says it learned of active exploitation in October 2026, and CISA added it to KEV on October 29 with a November 1 federal deadline. Repeated crashes mean repeated VPN and firewall outages; crashes can also be used to cover other activity. Am I affected (all must be true): - SSL VPN is enabled: the config has webvpn with enable <interface> on at least one interface, and the login page is reachable. - Secondary authentication is configured on a tunnel group: with tunnel-group-list enable, any tunnel group (including DefaultWEBVPNGroup) that has secondary-authentication-server-group; without a group list, DefaultWEBVPNGroup with secondary authentication. - On FTD, check the deployed remote access VPN policy in FMC or FDM. Cloud-delivered Firewall, cdFMC, Secure Access and FMC software are not affected. Fix: 1. Upgrade to a first fixed release (or later): ASA 9.16.4.104, 9.18.4.96, 9.20.4.50, 9.22.3.200, 9.23.1.48, 9.24.1.27 / 9.24.10.1; FTD 7.0.11, 7.2.13, 7.4.9, 7.6.7, 7.7.14, 10.0.3, 10.1.1. Use Cisco's Software Checker to confirm for your exact release. 2. Temporary mitigation from Cisco until you can upgrade: if DefaultWEBVPNGroup does not use secondary authentication, run no tunnel-group-list enable (users then must use the correct connection profile URL); if it does, Cisco's alternative is removing secondary-authentication-server-group, which weakens VPN login security, so prefer upgrading quickly. 3. Watch for unexpected reloads (show version uptime, crash files, syslog) and treat repeated crashes as an attack in progress. Verify: show version reports a fixed release, and show running-config tunnel-group / webvpn reflects any mitigation you applied. Sources: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-tunnel-dos-s6mgkb75 https://www.cisa.gov/known-exploited-vulnerabilities-catalog https://nvd.nist.gov/vuln/detail/CVE-2026-76418

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