CVE-2026-20349: Cisco ASA and FTD remote-access VPN denial of service

Quick Answer

CISA added CVE-2026-20349 to its Known Exploited Vulnerabilities catalog on 2026-08-11, confirming that exploitation has occurred. If you operate Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD), identify the exact version and relevant configuration now, preserve security evidence, and follow the live vendor remediation. A KEV match does not prove your system was compromised, and installing an update does not rule out earlier exploitation.

Last verified: 2026-09-17 UTC. CISA KEV snapshot version 2026.09.16. Recheck the live advisory before changing production.

Context

Status At A Glance

Product scope	Cisco — Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD)
CVE	CVE-2026-20349
TechGeeks response tier	P0 — confirm an exact match and act now
CISA KEV added	2026-08-11
Vendor severity	High
CVSS	CVSS 3.1 base 8.6 — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Ransomware field	Unknown — this is not the same as No; CISA has not marked the field Known.
Forensic-triage field	No in the current CISA field; organizations should still investigate when exposure or evidence warrants it.
CWE	CWE-244
Federal remediation date	2026-08-14 — applies to covered federal agencies; other organizations should set a risk-based deadline.

What Happened

Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection Vulnerability. Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) contain a heap inspection vulnerability that could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. CISA's KEV listing confirms exploitation evidence, but it does not state how widespread the activity is or prove that any particular installation was compromised.

Affected Scope

Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) contain a heap inspection vulnerability that could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition.

Match the exact edition, hardware or virtual platform, release, patch level, enabled feature, and management exposure. A product-family name alone is not enough to establish applicability.

Steps

What To Do Now

1. Confirm. Inventory every Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) asset and record its exact version, patch level, role, relevant configuration, and exposure.
2. Preserve. Save UTC timestamps, off-device authentication, firewall, proxy, DNS, endpoint, application, and SIEM evidence before logs rotate or a disruptive change removes context.
3. Contain. Restrict unnecessary internet and management-plane access using supported controls. Follow the live advisory: Open the live Cisco advisory.
4. Remediate. Confirm whether SSL VPN, IKEv2 client services, or ZTNA enables a vulnerable listener; upgrade ASA or FTD to the fixed hardening release for its train.
5. Validate. Verify the resulting version or patch level, service health, logging, expected access, an expected denial, and representative dependent workflows.
6. Escalate. If exposure overlapped the vulnerable period or evidence is suspicious, treat the system as a potential incident and follow vendor and incident-response recovery guidance.

Fixed Releases And Mitigation

Verified fixed release, patch level, or update guidance captured at the last check:

• ASA 9.16.4.103
• ASA 9.18.4.94
• ASA 9.20.4.49
• ASA 9.22.3.26
• ASA 9.23.1.47
• ASA 9.24.1.26
• FTD 7.0.10
• FTD 7.2.12
• FTD 7.4.8
• FTD 7.6.6
• FTD 7.7.13
• FTD 10.0.2
• FTD 10.1.0

Mitigation boundary: Cisco says there is no workaround. Disable unnecessary vulnerable remote-access services while arranging the upgrade, where operationally acceptable.

A workaround, access restriction, or provider-side control reduces a described path; it does not necessarily remove vulnerable code or erase compromise.

Investigation And Recovery

CISA's KEV record does not mark this entry for forensic triage. That field is not proof of a clean system; consult the vendor advisory for indicators and recovery guidance.

When an attacker may have gained administrative, root, SYSTEM, identity, management-plane, or code-execution access, patching alone is not an eradication claim. Preserve evidence, scope affected accounts and downstream systems, rotate exposed credentials or certificates when justified, and rebuild from a trusted source when vendor or incident-response guidance requires it.

Notes

Exploitation Evidence

Vendor statement: Cisco PSIRT became aware of active exploitation in August 2026.

CISA statement: CVE-2026-20349 was added to KEV on 2026-08-11. The ransomware field is Unknown, and the forensic-triage field is No. These are separate signals.

Validation And Boundaries

This notice does not prove that every product carrying the family name is affected, that exploitation is widespread, that a clean indicator search rules out compromise, or that a successful update restored trust. TechGeeks has not reproduced the exploit and does not replace the vendor advisory, asset inventory, vulnerability scanner, or incident-response process.

Related TechGeeks Resources

• Security Hot Page
• All Security Notices
• What to Do When a Device Hits CISA KEV
• Router CVE Exposure, Version, and Mitigation Checklist
• IoT Firmware Update and End-of-Support Checklist
• Live Protect and Runtime Vulnerability Shielding

References

• Cisco advisory or support notice
• CISA guidance
• CISA guidance
• NVD CVE record
• CISA source

Wrap-Up

Record whether CVE-2026-20349 applies to your environment. If it does, assign an owner, preserve the change and investigation evidence, complete the vendor action, and document the validated result.

Correction policy: If a primary source changes affected versions, remediation, exploitation status, or recovery guidance, TechGeeks will update this page and its verification date.