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Cisco patches ASA and FTD VPN flaw used to crash firewalls
Cisco said Wednesday that CVE-2026-76418, a high-severity SSL VPN denial-of-service bug in ASA and FTD software, is being exploited in the wild, The Hacker News and BleepingComputer reported.
Cisco on Wednesday published patches for a high-severity bug in Secure Firewall Adaptive Security Appliance and Threat Defense software that the company said attackers are already using to crash devices over SSL remote-access VPN1,2.
The flaw, CVE-2026-76418, is scored 8.6 on CVSS1. Cisco said an unauthenticated remote attacker can send a crafted request while connecting to SSL VPN and force an unexpected reload, a denial-of-service condition1,2.
The company attributed the issue to logic errors when secondary authentication is configured on a tunnel group1,2. BleepingComputer said affected setups include the webvpn keyword with SSL VPN enabled on at least one interface2.
Cisco's Product Security Incident Response Team said it became aware of active exploitation in October 20261,2. Neither report named operators, victims, or the scale of attacks, and Cisco did not publish indicators of compromise1,2.
The Hacker News listed first fixed ASA releases including 9.16.4.104, 9.18.4.96, 9.20.4.50, 9.22.3.200, 9.23.1.48, and 9.24.1.27 or 9.24.10.1, and FTD fixes including 7.0.11, 7.2.13, 7.4.9, 7.6.7, 7.7.14, 10.0.3, and 10.1.11.
Cisco said a device is in scope if it runs a vulnerable ASA or FTD release, the SSL remote-access VPN login is reachable, and secondary authentication is set in the relevant tunnel-group scope, including DefaultWEBVPNGroup when the group list is disabled1.
Cisco said there is no complete workaround2. As a temporary mitigation, it recommended disabling the tunnel-group list if DefaultWEBVPNGroup does not use secondary authentication, or turning off secondary authentication on user-configured tunnel groups1,2.
BleepingComputer cited internet-monitoring firm Shadowserver as tracking more than 51,000 Cisco ASA SSL VPN devices online, without saying how many are patched or honeypots2.
The same outlet noted earlier ASA and FTD VPN flaws, including 2025 bugs that CISA answered with Emergency Directive 25-03 and that Cisco linked to the ArcaneDoor campaign2. Those earlier bugs are separate from CVE-2026-76418; Cisco has not attributed this month's crashes to that campaign1,2.
Sources
How it’s being reported
2 sourcesFirst reported by 
The Hacker News
The Hacker NewsFirstCisco Patches Actively Exploited ASA and FTD VPN Flaw That Can Crash Firewalls
CVSS 8.6, fixed version lists, and the exact tunnel-group conditions Cisco says make a device exposed.
Cisco released patches for CVE-2026-76418, an 8.6 CVSS SSL VPN logic flaw that can reload ASA and FTD devices when secondary authentication is set on a tunnel group.
Leaves out Shadowserver internet-exposure count and last year's ArcaneDoor / CISA directive history.
New Cisco firewall zero-day exploited to crash SSL VPN devices
Zero-day framing, lack of IoCs, Shadowserver exposure, and prior ASA/FTD campaigns including ArcaneDoor.
Cisco patched an unauthenticated DoS zero-day in ASA and FTD SSL VPN after PSIRT saw in-the-wild use this month; Shadowserver counts more than 51,000 exposed ASA SSL VPNs.
Leaves out The full per-branch first-fixed version table published by Cisco and The Hacker News.
Where they agree
- CVE-2026-76418 is a high-severity unauthenticated remote DoS in ASA/FTD SSL VPN.
- Cisco PSIRT learned of active exploitation in October 2026.
- Root cause is logic errors with secondary authentication on a tunnel group.
- Cisco released software fixes and described a secondary-auth mitigation, not a full workaround.