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Used in attacks· fix by 2026-08-148.6High

Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD)

CVE-2026-20349

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.

What this means for your business

  • It affects Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD). It matters if your company, or a supplier that handles your data, runs it.
  • Attackers are already using it. CISA added it to its list of flaws used in real attacks on 11 August 2026.
  • An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 1% chance of attack attempts being seen in the next 30 days, ranking above 63% of all known flaws.

What to do

  1. 1Check whether your company or your suppliers run Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD), and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
  3. 3Treat it as urgent. US federal agencies must fix it by 14 August 2026. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
  4. 4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.

Fastnexa security experts

Attackers are already using this flaw. Is your Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) exposed?

Tell us where you run Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) and a Fastnexa penetration tester will check whether this flaw, or others like it, can be used against your websites, apps and network.

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Required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

CISA’s wording, unedited. The notes it mentions are in CISA’s catalogue entry.

Scoring

CVSS
8.6 (v3.1)
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Weakness
CWE-244
Assigned by
psirt@cisco.com

Dates

Published
2026-08-11
Last modified
2026-09-16
Added to KEV
2026-08-11
Remediation due
2026-08-14
Sources
CISA KEV, NVD

Affected products

  • Cisco Adaptive Security Appliance Software9.16.1, 9.16.1.28, 9.16.2, 9.16.2.3, 9.16.2.7, 9.16.2.11, 9.16.2.13, 9.16.2.14, 9.16.3, 9.16.3.3, 9.16.3.14, 9.16.3.15, 9.16.3.19, 9.16.3.23, 9.16.4, 9.16.4.9, 9.16.4.14, 9.16.4.19, 9.16.4.27, 9.16.4.38, 9.16.4.39, 9.16.4.42, 9.16.4.48, 9.16.4.55, 9.16.4.57, 9.16.4.61, 9.16.4.62, 9.16.4.67, 9.16.4.70, 9.16.4.71, 9.16.4.76, 9.16.4.82, 9.16.4.84, 9.16.4.85, 9.16.4.89, 9.16.4.92, 9.18.1, 9.18.1.3, 9.18.2, 9.18.2.5, 9.18.2.7, 9.18.2.8, 9.18.3, 9.18.3.39, 9.18.3.46, 9.18.3.53, 9.18.3.55, 9.18.3.56, 9.18.4, 9.18.4.5, 9.18.4.8, 9.18.4.22, 9.18.4.24, 9.18.4.29, 9.18.4.34, 9.18.4.40, 9.18.4.47, 9.18.4.50, 9.18.4.52, 9.18.4.53, 9.18.4.57, 9.18.4.66, 9.18.4.67, 9.18.4.68, 9.18.4.71, 9.18.4.76, 9.18.4.82, 9.18.4.90, 9.18.4.135, 9.19.1, 9.19.1.5, 9.19.1.9, 9.19.1.12, 9.19.1.18, 9.19.1.22, 9.19.1.24, 9.19.1.27, 9.19.1.28, 9.19.1.31, 9.19.1.37, 9.19.1.38, 9.19.1.42, 9.20.1, 9.20.1.5, 9.20.2, 9.20.2.10, 9.20.2.21, 9.20.2.22, 9.20.3, 9.20.3.4, 9.20.3.7, 9.20.3.9, 9.20.3.10, 9.20.3.13, 9.20.3.16, 9.20.3.20, 9.20.4, 9.20.4.7, 9.20.4.10, 9.20.4.14, 9.20.4.19, 9.20.4.22, 9.20.4.28, 9.20.4.30, 9.20.4.34, 9.20.4.46, 9.22.1.1, 9.22.1.2, 9.22.1.3, 9.22.1.6, 9.22.2, 9.22.2.4, 9.22.2.9, 9.22.2.13, 9.22.2.14, 9.22.2.20, 9.22.2.32, 9.22.3, 9.22.3.5, 9.23.1, 9.23.1.3, 9.23.1.7, 9.23.1.13, 9.23.1.19, 9.23.1.22, 9.23.1.26, 9.23.1.32, 9.23.1.195, 9.24.1, 9.24.1.5, 9.24.1.9, 9.24.1.11, 9.24.1.155
  • Cisco Secure Firewall Threat Defense7.0.0, 7.0.0.1, 7.0.1, 7.0.1.1, 7.0.2, 7.0.2.1, 7.0.3, 7.0.4, 7.0.5, 7.0.6, 7.0.6.1, 7.0.6.2, 7.0.6.3, 7.0.7, 7.0.8, 7.0.8.1, 7.0.9, 7.2.0, 7.2.0.1, 7.2.1, 7.2.2, 7.2.3, 7.2.4, 7.2.4.1, 7.2.5, 7.2.5.1, 7.2.5.2, 7.2.6, 7.2.7, 7.2.8, 7.2.8.1, 7.2.9, 7.2.10, 7.2.10.2, 7.2.11, 7.2.12, 7.3.0, 7.3.1, 7.3.1.1, 7.3.1.2, 7.4.0, 7.4.1, 7.4.1.1, 7.4.2, 7.4.2.1, 7.4.2.2, 7.4.2.3, 7.4.2.4, 7.4.3, 7.4.4, 7.4.7, 7.4.8, 7.6.0, 7.6.1, 7.6.2, 7.6.2.1, 7.6.4, 7.7.0, 7.7.10, 7.7.10.1, 7.7.11, 7.7.13, 10.0.0, 10.0.2

As listed in the NVD configuration data. Not a statement about your estate.

References