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

Quick assessment

Affected
Cisco Cisco Secure Firewall Threat Defense (FTD) Software
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Cisco 安全防火墙威胁防御（FTD）软件中 TLS 1.3 实现存在一个漏洞，未认证的远程攻击者可借此使受影响的设备意外重新加载，从而导致拒绝服务（DoS）状况。 该漏洞源于 TLS 1.3 连接过程中的缓冲区管理不当。攻击者可通过在启用了 TLS 1.3 的监听套接字上向受影响系统发送构造的 TLS 1.3 数据包来利用此漏洞。若利用成功，可导致 LINA 进程崩溃，进而触发设备重新加载。该重新加载可能发生在连接认证之前或之后。 注意：TLS 1.3 连接同时包括数据流量和用户管理流量。

CVSS 8.6 · High EPSS 0.46% · P39

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 58

VendorProduct Version RangeStatus
Cisco Cisco Secure Firewall Threat Defense (FTD) Software 7.0.0 affected
7.0.0.1 affected
7.0.1 affected
7.0.1.1 affected
7.0.2 affected
7.2.0 affected
7.0.2.1 affected
7.0.3 affected
… +50 more rows
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I. Basic Information for CVE-2026-20135

Vulnerability Information
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Vulnerability Title
Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability
Source: CVE Program / CVE List V5
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
双重释放
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Cisco Cisco Secure Firewall Threat Defense (FTD) Software 7.0.0 -

II. Public POCs for CVE-2026-20135

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III. Intelligence Information for CVE-2026-20135

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Vendor Advisories for CVE-2026-20135 (1)

Same Patch Batch · Cisco · 2026-09-16 · 79 CVEs total

CVE-2026-20192 10.0 CRITICAL Cisco Identity Services Engine Hardening Release - Access Control Vulnerabilities
CVE-2026-76460 10.0 CRITICAL Cisco Identity Services Engine Authentication Bypass Vulnerability
CVE-2026-76423 10.0 CRITICAL Cisco ISE API Authentication Bypass Vulnerability
CVE-2026-20130 10.0 CRITICAL Cisco Identity Services Engine Hardening Release - Improper Neutralization Vulnerabilities
CVE-2026-20332 9.9 CRITICAL Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software
CVE-2026-20307 9.9 CRITICAL Cisco Identity Services Engine Remote Code Execution Vulnerability
CVE-2026-20234 9.9 CRITICAL Cisco Identity Services Engine Hardening Release - Insuffiencently Protected Credential Vu
CVE-2026-20324 9.9 CRITICAL Cisco Secure Firewall Management Center sftunnel Root Arbitrary Code Exectution Vulnerabil
CVE-2026-20325 9.9 CRITICAL Cisco Nexus Dashboard Software Security Hardening Release September 2026 - Improper Neutra
CVE-2026-20329 9.9 CRITICAL Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software
CVE-2026-20322 9.9 CRITICAL Cisco Nexus Dashboard Software Security Hardening Release September 2026 - Improper Access
CVE-2026-20330 9.9 CRITICAL Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software
CVE-2026-20242 9.8 CRITICAL Cisco Secure Firewall Management Center Software Java Deserialization Remote Code Executio
CVE-2026-20326 9.8 CRITICAL Cisco Nexus Dashboard Software Security Hardening Release September 2026 - Missing Authent
CVE-2026-20331 9.6 CRITICAL Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software
CVE-2026-20306 9.1 CRITICAL Cisco Identity Services Engine Command Injection Vulnerability
CVE-2026-20211 9.1 CRITICAL Cisco Identity Services Engine Remote Code Execution Vulnerability
CVE-2026-20341 9.1 CRITICAL Cisco Secure Firewall Management Center Software sftunnel Deserialization Root Command Exe
CVE-2026-20176 9.1 CRITICAL Cisco Identity Services Engine Remote Code Execution Vulnerability
CVE-2026-20284 9.1 CRITICAL Cisco Identity Search Engine SXP REST API SQL Injection Vulnerability

Showing top 20 of 79 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Cisco Secure Firewall Threat Defense (FTD) Software
Same vendor: Cisco
Same weakness: CWE-415

V. Comments for CVE-2026-20135

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