CVE-2026-76418

Think of this like a doorbell that, when pressed in a very specific odd way, makes the whole building's power trip. Here, a specially crafted connection request to the firewall's VPN login can make the firewall itself restart, cutting off remote access and any traffic passing through it until it comes back online.

This matters to you if you run Cisco Secure Firewall ASA or Secure Firewall Threat Defense software and use its Remote Access SSL VPN feature with secondary authentication configured on a tunnel group. If you don't use SSL VPN remote access on these devices, or don't use secondary authentication on a tunnel group, you are not exposed. This is reachable by anyone on the internet who can reach the VPN login, no account needed.

A working exploit for this is already publicly available, meaning attackers with technical skill could target exposed devices today, even though there's no confirmed evidence yet of it being used in real-world attacks. Combined with the lack of a vendor fix, this warrants prompt attention and mitigation rather than a wait-and-see approach, but it is not yet a confirmed active-attack emergency.

Confirm exposure by checking Cisco ASA/FTD configuration for Remote Access SSL VPN with secondary authentication enabled on any tunnel group; this is the specific trigger condition per the advisory. No fixed software version has been published by Cisco for either ASA or FTD at this time — monitor Cisco's Security Advisories page for updates and apply the patch immediately once released. As a temporary workaround while unpatched, consider disabling secondary authentication on affected tunnel groups or restricting SSL VPN access to trusted source IPs/VPN concentrators behind additional filtering, understanding this may reduce authentication assurance. Monitor device logs for unexpected reloads correlating with VPN connection attempts, and track public exploit code repositories/advisory updates since a PoC is already circulating, which increases near-term risk even though CISA KEV listing and confirmed in-the-wild exploitation have not yet occurred.

CVSS 3.1 score 8.6 (High), vector AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H — network-exploitable, low complexity, no privileges or user interaction required, scope changed, availability impact high (device crash/reload), no confidentiality/integrity impact. Weakness is CWE-690 (unchecked return value leading to NULL pointer or improper handling), triggered via logic errors in secondary authentication processing on SSL VPN tunnel groups. EPSS predicts low near-term exploitation likelihood with a flat trend; not listed in CISA KEV; a public exploit exists, indicating moderate exploit maturity (PoC/weaponized code available) but no confirmed in-the-wild attacks reported. No patch is currently available from Cisco.