CVE-2026-20323: Cisco Secure Firewall Management Center and Secure Firewall Threat Defense Software sftunnel Unauthorized Authentication Bypass Vulnerability
A vulnerability in the sftunnel inter-device communication protocol of Cisco Secure FMC Software and Cisco Secure FTD Software could allow an unauthenticated, adjacent attacker to impersonate the peer device and obtain access at the level of the manager role, which is equivalent to root. This vulnerability is due to improper management of the TLS certificate for the sftunnel management connection. An attacker could exploit this vulnerability by connecting to the sftunnel port using a crafted TLS certificate. A successful exploit could allow the attacker to become a registered sftunnel peer with root access. Note: The attack is successful only if the sftunnel connection is down or the attack can disrupt the sftunnel connection long enough to execute the attack.
Affected Software
Event History
Frequently Asked Questions
Who can exploit this vulnerability?
An attacker must be adjacent to the affected device and does not need prior authentication or user interaction. Successful exploitation lets the attacker impersonate the peer device and gain manager-role access, equivalent to root.
What conditions are required for exploitation?
The attacker must connect to the sftunnel port with a crafted TLS certificate. The sftunnel connection must also be down, or the attacker must be able to disrupt it long enough to carry out the attack.
How can I determine whether an attack may have succeeded?
A successful attack results in an unauthorized device becoming a registered sftunnel peer with root-level access. Review registered sftunnel peers and investigate unexpected peer registrations, especially following sftunnel connection outages or disruptions.