CVE-2026-76418 in Secure Firewall Adaptive Security Appliance
Summary
by MITRE • 10/28/2026
A vulnerability in the Remote Access SSL VPN service 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 the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to logic errors when secondary authentication is configured on a tunnel group. 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.
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Analysis
by VulDB Data Team • 10/28/2026
The identified security flaw resides within the Remote Access Secure Sockets Layer Virtual Private Network service implemented in Cisco Secure Firewall Adaptive Security Appliance Software and Cisco Secure Firewall Threat Defense Software. This vulnerability stems from specific logic errors that occur when secondary authentication mechanisms are configured on a tunnel group configuration object. The root cause is not related to buffer overflows or memory corruption but rather an incorrect handling of state transitions during the authentication handshake process, which leads to unstable system behavior under certain conditions.
An unauthenticated remote attacker can exploit this vulnerability by establishing a connection to the SSL remote access VPN and sending specially crafted requests that trigger the flawed logic path within the secondary authentication module. Because the attack vector requires no prior credentials or successful login, it is classified as an unauthenticated remote exploitation scenario. The attacker does not need elevated privileges on the target system; they merely need network connectivity to the vulnerable service endpoint and the ability to send packets containing specific malformed data structures that confuse the state machine managing the authentication session.
The operational impact of a successful exploit is severe, resulting in an unexpected reload or reboot of the affected firewall device. This action directly causes a denial of service condition for all users relying on the network infrastructure protected by the appliance. The sudden restart disrupts active sessions, drops ongoing traffic flows, and may cause temporary loss of connectivity to critical services hosted behind the firewall. Furthermore, frequent reboots can lead to hardware wear over time and complicate incident response efforts due to potential log rotation or clearing during the reboot process, making forensic analysis more difficult for security teams attempting to trace the attack origin.
From a classification perspective, this vulnerability aligns with CWE-841 Improper Enforcement of Behavioral Workflow, as the software fails to correctly enforce the expected sequence of operations during secondary authentication. In terms of tactical mapping within the MITRE ATT&CK framework, this exploit falls under Initial Access techniques involving Exploitation for Remote Code Execution or Denial of Service, specifically leveraging network service vulnerabilities to disrupt availability rather than gaining persistent access. The lack of required authentication makes it particularly dangerous in environments where SSL VPN services are exposed directly to untrusted networks such as the public internet without additional perimeter controls like IP allow-listing.
Mitigation strategies should prioritize applying the vendor-provided software patches that address the logic error in the secondary authentication module immediately upon availability. In scenarios where patching is not immediately feasible, administrators can implement network-level access control lists to restrict source IP addresses allowed to connect to the SSL VPN service, thereby limiting exposure to only trusted networks. Additionally, disabling secondary authentication if it is not strictly required for the specific use case may reduce the attack surface, although this should be weighed against security policy requirements. Continuous monitoring of system logs for unexpected reload events and configuring alerting mechanisms can help detect potential exploitation attempts or their aftermath in real-time, allowing for rapid incident response.