CVE-2026-20135: Double Free in Cisco Cisco Secure Firewall Threat Defense (FTD) Software
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.
AI Analysis
Technical Summary
This vulnerability arises from a double free condition in the TLS 1.3 implementation of Cisco Secure Firewall Threat Defense (FTD) Software. An attacker can exploit this by sending specially crafted TLS 1.3 packets to a TLS 1.3-enabled listening socket, causing improper buffer management that crashes the LINA process. The crash forces the device to reload, resulting in a denial of service. The vulnerability affects multiple specific versions of Cisco Secure Firewall Threat Defense (FTD) Software as enumerated. The CVSS v3.1 score is 8.6, indicating high severity with network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability.
Potential Impact
Exploitation leads to denial of service by causing the LINA process to crash and the device to reload unexpectedly. This disrupts firewall operations and potentially network security monitoring or enforcement. There is no impact on confidentiality or integrity reported. The vulnerability can be triggered remotely without authentication.
Mitigation Recommendations
Patch status is not yet confirmed — check the Cisco vendor advisory for current remediation guidance. No official fix or patch links are provided in the available data. Until a patch is available, consider disabling TLS 1.3 if feasible or restricting access to TLS 1.3-enabled listening sockets to trusted sources to reduce exposure.
CVE-2026-20135: Double Free in Cisco Cisco Secure Firewall Threat Defense (FTD) Software
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.
CVSS v3.1
Score 8.6high
Affected software
Cisco
Cisco Secure Firewall Threat Defense (FTD) Software
pkg:github/cisco/secure-firewall-threat-defenseRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability arises from a double free condition in the TLS 1.3 implementation of Cisco Secure Firewall Threat Defense (FTD) Software. An attacker can exploit this by sending specially crafted TLS 1.3 packets to a TLS 1.3-enabled listening socket, causing improper buffer management that crashes the LINA process. The crash forces the device to reload, resulting in a denial of service. The vulnerability affects multiple specific versions of Cisco Secure Firewall Threat Defense (FTD) Software as enumerated. The CVSS v3.1 score is 8.6, indicating high severity with network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability.
Potential Impact
Exploitation leads to denial of service by causing the LINA process to crash and the device to reload unexpectedly. This disrupts firewall operations and potentially network security monitoring or enforcement. There is no impact on confidentiality or integrity reported. The vulnerability can be triggered remotely without authentication.
Mitigation Recommendations
Patch status is not yet confirmed — check the Cisco vendor advisory for current remediation guidance. No official fix or patch links are provided in the available data. Until a patch is available, consider disabling TLS 1.3 if feasible or restricting access to TLS 1.3-enabled listening sockets to trusted sources to reduce exposure.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- cisco
- Date Reserved
- 2025-10-08T11:59:15.381Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6aab006655bf5e2cf5231fff
Added to database: 09/16/2026, 20:47:34 UTC
Last enriched: 09/16/2026, 21:31:53 UTC
Last updated: 09/17/2026, 03:01:24 UTC
Views: 6
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