CVE-2026-20248 Cisco CVE debrief

Who should care

Network administrators and security teams responsible for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software should assess exposure and prioritize verification of DNS query handling and device reload vulnerabilities.

Why it matters

Network administrators and security teams should assess exposure and prioritize verification of DNS query handling and device reload vulnerabilities in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software due to potential denial of service (DoS) conditions and disruption of network operations and services.

• Denial of service (DoS) condition due to device reload
• Potential disruption of network operations and services
• Need for verification of DNS query handling and device reload vulnerabilities
• Potential for exploitation by unauthenticated, remote attackers

Technical summary

The vulnerability is due to a logic error when parsing a DNS query and tracking the size of the incoming buffers. An attacker could exploit this vulnerability by formatting a crafted reply to a DNS query sent from the targeted device. This vulnerability affects Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software, which are used in various network environments. Network administrators and security teams should assess exposure and prioritize verification of DNS query handling and device reload vulnerabilities.

Defensive priority

Network administrators and security teams should assess exposure and prioritize verification of DNS query handling and device reload vulnerabilities in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software.

Recommended defensive actions

• Verify DNS query handling and device reload vulnerabilities in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software
• Assess exposure and prioritize verification of DNS query handling and device reload vulnerabilities
• Review and update incident response plans to address potential denial of service (DoS) conditions
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and potential impact. However, the corpus does not establish versions, exploitation, impact, or remediation, which require verification from the supplied official sources.

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.