CVE-2026-20135
Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability
Description
A vulnerability in the TLS 1.3 implementation in Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper buffer management during the TLS 1.3 connection. An attacker could exploit this vulnerability by sending a crafted TLS 1.3 packet to an affected system through a TLS 1.3-enabled listening socket. A successful exploit could allow the attacker to cause the LINA process to crash, which would cause the device to reload. The reload can happen before or after authentication of the connection.Note: TLS 1.3 connections include both data traffic and user-management traffic.
Weakness: CWE-415
Affected products
| Vendor | Product | Category | Matched by |
|---|---|---|---|
| Cisco | Cisco Firepower Threat Defense (FTD) Check your version | Firewall / NGFW | cna-assigner |
Vendor-reported products (1)
- Cisco · Cisco Secure Firewall Threat Defense (FTD) Software
Vendor advisory
cisco-sa-ftd-tls1.3-dos-dLxwFWgF
Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability
Cisco’s rating: High (advisory CVSS 8.6) · Published Sep 16, 2026
Bug ID: CSCwo83926
The vendor’s rating applies to the whole advisory and can differ from this CVE’s own CVSS severity. Where this comes from