Cisco Secure Firewall Threat Defense up to 7.7.11 TLS 1.3 Implementation denial of service

Summaryinfo

A vulnerability marked as critical has been reported in Cisco Secure Firewall Threat Defense. The impacted element is an unknown function of the component TLS 1.3 Implementation. The manipulation leads to denial of service. This vulnerability is listed as CVE-2026-20135. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Cisco Secure Firewall Threat Defense and classified as critical. This issue affects an unknown code of the component TLS 1.3 Implementation. The manipulation with an unknown input leads to a denial of service vulnerability. Using CWE to declare the problem leads to CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. Impacted is availability. The summary by CVE is:

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.

The advisory is shared at sec.cloudapps.cisco.com. The identification of this vulnerability is CVE-2026-20135 since 10/08/2025. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/16/2026). MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Firewall Software

Vendor

• Cisco

Name

• Secure Firewall Threat Defense

Version

• 7.0.0
• 7.0.0.1
• 7.0.1
• 7.0.1.1
• 7.0.2
• 7.0.2.1
• 7.0.3
• 7.0.4
• 7.0.5
• 7.0.6
• 7.0.6.1
• 7.0.6.2
• 7.0.6.3
• 7.0.7
• 7.0.8
• 7.0.8.1
• 7.0.9
• 7.2.0
• 7.2.0.1
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.4.1
• 7.2.5
• 7.2.5.1
• 7.2.5.2
• 7.2.6
• 7.2.7
• 7.2.8
• 7.2.8.1
• 7.2.9
• 7.2.10
• 7.2.10.2
• 7.2.11
• 7.3.0
• 7.3.1
• 7.3.1.1
• 7.3.1.2
• 7.4.0
• 7.4.1
• 7.4.1.1
• 7.4.2
• 7.4.2.1
• 7.4.2.2
• 7.4.2.3
• 7.4.2.4
• 7.4.3
• 7.4.4
• 7.6.0
• 7.6.1
• 7.6.2
• 7.6.2.1
• 7.6.4
• 7.7.0
• 7.7.10
• 7.7.10.1
• 7.7.11

License

• commercial

Website

• Vendor: https://www.cisco.com/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion