CVE-2026-20135 - Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability

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HIGH

Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability

Published Sep 16, 2026

8.6

HIGH

CVSS 3.1

EPSS 0.46%

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.

Affected products

Vendor Cisco Product Cisco Secure Firewall Threat Defense (FTD) Software Default
n/a
- Version
  7.0.0
  Status
  affected
  Constraints
  -
- Version
  7.0.0.1
  Status
  affected
  Constraints
  -
- Version
  7.0.1
  Status
  affected
  Constraints
  -
- Version
  7.0.1.1
  Status
  affected
  Constraints
  -
- Version
  7.0.2
  Status
  affected
  Constraints
  -
- Version
  7.0.2.1
  Status
  affected
  Constraints
  -
- Version
  7.0.3
  Status
  affected
  Constraints
  -
- Version
  7.0.4
  Status
  affected
  Constraints
  -
- Version
  7.0.5
  Status
  affected
  Constraints
  -
- Version
  7.0.6
  Status
  affected
  Constraints
  -
- Version
  7.0.6.1
  Status
  affected
  Constraints
  -
- Version
  7.0.6.2
  Status
  affected
  Constraints
  -
- Version
  7.0.6.3
  Status
  affected
  Constraints
  -
- Version
  7.0.7
  Status
  affected
  Constraints
  -
- Version
  7.0.8
  Status
  affected
  Constraints
  -
- Version
  7.0.8.1
  Status
  affected
  Constraints
  -
- Version
  7.0.9
  Status
  affected
  Constraints
  -
- Version
  7.2.0
  Status
  affected
  Constraints
  -
- Version
  7.2.0.1
  Status
  affected
  Constraints
  -
- Version
  7.2.1
  Status
  affected
  Constraints
  -
- Version
  7.2.10
  Status
  affected
  Constraints
  -
- Version
  7.2.10.2
  Status
  affected
  Constraints
  -
- Version
  7.2.11
  Status
  affected
  Constraints
  -
- Version
  7.2.2
  Status
  affected
  Constraints
  -
- Version
  7.2.3
  Status
  affected
  Constraints
  -
- Version
  7.2.4
  Status
  affected
  Constraints
  -
- Version
  7.2.4.1
  Status
  affected
  Constraints
  -
- Version
  7.2.5
  Status
  affected
  Constraints
  -
- Version
  7.2.5.1
  Status
  affected
  Constraints
  -
- Version
  7.2.5.2
  Status
  affected
  Constraints
  -
- Version
  7.2.6
  Status
  affected
  Constraints
  -
- Version
  7.2.7
  Status
  affected
  Constraints
  -
- Version
  7.2.8
  Status
  affected
  Constraints
  -
- Version
  7.2.8.1
  Status
  affected
  Constraints
  -
- Version
  7.2.9
  Status
  affected
  Constraints
  -
- Version
  7.3.0
  Status
  affected
  Constraints
  -
- Version
  7.3.1
  Status
  affected
  Constraints
  -
- Version
  7.3.1.1
  Status
  affected
  Constraints
  -
- Version
  7.3.1.2
  Status
  affected
  Constraints
  -
- Version
  7.4.0
  Status
  affected
  Constraints
  -
- Version
  7.4.1
  Status
  affected
  Constraints
  -
- Version
  7.4.1.1
  Status
  affected
  Constraints
  -
- Version
  7.4.2
  Status
  affected
  Constraints
  -
- Version
  7.4.2.1
  Status
  affected
  Constraints
  -
- Version
  7.4.2.2
  Status
  affected
  Constraints
  -
- Version
  7.4.2.3
  Status
  affected
  Constraints
  -
- Version
  7.4.2.4
  Status
  affected
  Constraints
  -
- Version
  7.4.3
  Status
  affected
  Constraints
  -
- Version
  7.4.4
  Status
  affected
  Constraints
  -
- Version
  7.6.0
  Status
  affected
  Constraints
  -
- Version
  7.6.1
  Status
  affected
  Constraints
  -
- Version
  7.6.2
  Status
  affected
  Constraints
  -
- Version
  7.6.2.1
  Status
  affected
  Constraints
  -
- Version
  7.6.4
  Status
  affected
  Constraints
  -
- Version
  7.7.0
  Status
  affected
  Constraints
  -
- Version
  7.7.10
  Status
  affected
  Constraints
  -
- Version
  7.7.10.1
  Status
  affected
  Constraints
  -
- Version
  7.7.11
  Status
  affected
  Constraints
  -

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor

Product

Default status

Versions

Cisco

Cisco Secure Firewall Threat Defense (FTD) Software

n/a

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

Remediation

No remediation recorded yet.

Weaknesses (1)

CWE-415

References (2)

Link	Providers	Tags
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-81123		Advisory
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tls1.3-dos-dLxwFWgF