CVE-2026-20006 Cisco CVE debrief

Who should care

Network administrators and security teams responsible for managing Cisco Secure Firewall Threat Defense systems should be aware of this vulnerability and take steps to mitigate it. They should review system configurations, update incident response plans, and conduct vulnerability scanning and asset inventory to ensure the security of their systems.

Technical summary

A vulnerability in the TLS cryptography functionality of the Snort 3 Detection Engine of Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to unexpectedly restart, resulting in a denial of service (DoS) condition. This vulnerability is due to improper implementation of the TLS protocol. An attacker could exploit this vulnerability by sending a crafted TLS packet to an affected system. A successful exploit could allow the attacker to cause a device that is running Cisco Secure FTD Software to drop network traffic, resulting in a DoS condition. Note: TLS 1.3 is not affected by this vulnerability.

Defensive priority

Network administrators and security teams should prioritize patching vulnerable Cisco Secure Firewall Threat Defense systems to prevent potential DoS attacks.

Recommended defensive actions

• Patch vulnerable Cisco Secure Firewall Threat Defense systems
• Monitor network traffic for suspicious activity
• Implement compensating controls to mitigate potential DoS attacks
• Review and update incident response plans
• Conduct vulnerability scanning and asset inventory
• Verify system configurations and settings
• Track and document remediation progress

Evidence notes

The vulnerability is due to improper implementation of the TLS protocol in the Snort 3 Detection Engine of Cisco Secure Firewall Threat Defense (FTD) Software. An attacker could exploit this vulnerability by sending a crafted TLS packet to an affected system, potentially causing a device to drop network traffic and resulting in a DoS condition. TLS 1.3 is not affected by this vulnerability.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.