Answer in brief
CVE-2026-20135 records a Unknown severity vulnerability in Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability. The current sources do not mark it as known exploited. The current feed maps Cisco/Cisco Secure Firewall Threat Defense (FTD) Software (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Cisco/Cisco Secure Firewall Threat Defense (FTD) Software (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Cisco/Cisco Secure Firewall Threat Defense (FTD) Softwaregeneric | 7.0.0 || 7.0.0.1 || 7.0.1 || 7.0.1.1 || 7.0.2 || 7.2.0 || 7.0.2.1 || 7.0.3 || 7.2.0.1 || 7.0.4 || 7.2.1 || 7.0.5 || 7.3.0 || 7.2.2 || 7.2.3 || 7.3.1 || 7.2.4 || 7.0.6 || 7.2.5 || 7.2.4.1 || 7.3.1.1 || 7.4.0 || 7.0.6.1 || 7.2.5.1 || 7.4.1 || 7.2.6 || 7.0.6.2 || 7.4.1.1 || 7.2.7 || 7.2.5.2 || 7.3.1.2 || 7.2.8 || 7.6.0 || 7.4.2 || 7.2.8.1 || 7.0.6.3 || 7.4.2.1 || 7.2.9 || 7.0.7 || 7.7.0 || 7.4.2.2 || 7.2.10 || 7.6.1 || 7.4.2.3 || 7.0.8 || 7.6.2 || 7.7.10 || 7.7.11 || 7.0.8.1 || 7.6.2.1 || 7.7.10.1 || 7.4.2.4 || 7.2.10.2 || 7.4.3 || 7.6.4 || 7.4.4 || 7.0.9 || 7.2.11 | Not reported |
Published upstream
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 16, 2026
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.
Quoted source text, attributed separately from HOL analysis.