What is CVE-2026-20349?
A vulnerability in the Remote Access SSL VPN service for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to insufficient error checking when processing HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to the Remote Access SSL VPN service on an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
Timeline
- 2026-08-11Published to the U.S. National Vulnerability Database (NVD)
- 2026-08-11Added to the CISA Known Exploited Vulnerabilities (KEV) catalog
- 2026-08-12NVD record last updated
- 2026-08-13First covered in a defend.network daily briefing
- 2026-08-14CISA federal remediation deadline (BOD 22-01)
CISA Known Exploited Vulnerability
Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection Vulnerability
Affected product
Cisco Secure Firewall Adaptive Security Appliance (ASA) And Secure Firewall Threat Defense (FTD)
NVD also lists CPE entries for: Cisco Adaptive Security Appliance Software, Cisco Secure Firewall Threat Defense
Remediation Steps
- Apply the vendor security update for Cisco Adaptive Security Appliance Software as a priority.
- Restrict network exposure of the affected service to trusted sources until patched.
- Review logs and detections for indicators of exploitation.
- Confirm fixed versions against the official vendor advisory before deploying.
References
- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-dzv4mQFF
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-20349
- https://nvd.nist.gov/vuln/detail/CVE-2026-20349
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 1 of September 2026 (September 7 – 13)
- Vulnerability Priority Report – Week 5 of August 2026 (August 31 – September 6)
- Vulnerability Priority Report – Week 4 of August 2026 (August 24 – 30)
- Vulnerability Priority Report – Week 3 of August 2026 (August 17 – 23)
- Vulnerability Priority Report – Week 2 of August 2026 (August 10 – 16)
- SharePoint auth bypass exploited; 737 Chrome VPN extensions abused; Microsoft patches 398 flaws (2026-08-14)
- Lazarus Windows zero-day, Adobe CVSS 10.0 patches, 737 malicious Chrome VPN extensions (2026-08-13)
Browse all tracked CVEs in the defend.network CVE database →