CVE-2026-20039

Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability

HIGH

8.6

CVSS Score

Published: March 4, 2026 at 05:17 PM UTC

Updated: August 11, 2026 at 07:58 PM UTC

2 products affected across 1 vendorAdaptive Security ApplianceSecure Firewall Threat Defense

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Severity

HIGH8.6

Exploit prediction

EPSS 0.4%

SSVC

No known exploit

Description

A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to ineffective memory management of the VPN web server. An attacker could exploit this vulnerability by sending a large number of crafted HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Adaptive Security Appliance · Cisco

95%

9.12.1 ≤ v < 9.16.4.849.17.1 ≤ v < 9.18.4.579.19.1 ≤ v < 9.20.3.169.22.1.1 ≤ v < 9.22.2.49.23.1 ≤ v < 9.23.1.39.12.1 9.12.1.2 9.12.1.3 9.12.2 9.12.2.1 9.12.2.4 9.12.2.5 9.12.2.9 9.12.3 9.12.3.12 9.12.3.2 9.12.3.7 9.12.3.9 9.12.4 9.12.4.10 9.12.4.13 9.12.4.18 9.12.4.2 9.12.4.24 9.12.4.26 9.12.4.29 9.12.4.30 9.12.4.35 9.12.4.37 9.12.4.38 9.12.4.39 9.12.4.4 9.12.4.40 9.12.4.41 9.12.4.47 9.12.4.48 9.12.4.50 9.12.4.52 9.12.4.54 9.12.4.55 9.12.4.56 9.12.4.58 9.12.4.62 9.12.4.65 9.12.4.67 9.12.4.7 9.12.4.8 9.16.1 9.16.1.28 9.16.2 9.16.2.11 9.16.2.13 9.16.2.14 9.16.2.3 9.16.2.7 9.16.3 9.16.3.14 9.16.3.15 9.16.3.19 9.16.3.23 9.16.3.3 9.16.4 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 9.16.4.9 9.17.1 9.17.1.10 9.17.1.11 9.17.1.13 9.17.1.15 9.17.1.20 9.17.1.30 9.17.1.33 9.17.1.39 9.17.1.45 9.17.1.46 9.17.1.7 9.17.1.9 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 9.18.4.22 9.18.4.24 9.18.4.29 9.18.4.34 9.18.4.40 9.18.4.47 9.18.4.5 9.18.4.50 9.18.4.52 9.18.4.53 9.18.4.8 9.19.1 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 9.19.1.5 9.19.1.9 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 9.20.3.10 9.20.3.13 9.20.3.4 9.20.3.7 9.20.3.9 9.22.1.1 9.22.1.2 9.22.1.3 9.22.1.6 9.22.2 9.23.1

Affected range stops below 9.16.4.84, so it looks safe — our inference, not a vendor statement

Affected range stops below 9.18.4.57, so it looks safe — our inference, not a vendor statement

Affected range stops below 9.20.3.16, so it looks safe — our inference, not a vendor statement

Affected range stops below 9.22.2.4, so it looks safe — our inference, not a vendor statement

Affected range stops below 9.23.1.3, so it looks safe — our inference, not a vendor statement

Secure Firewall Threat Defense · Cisco

95%

6.4.0 ≤ v < 7.0.97.1.0 ≤ v < 7.2.107.3.0 ≤ v < 7.4.37.6.0 ≤ v < 7.6.17.7.0 ≤ v < 7.7.106.4.0 6.4.0.1 6.4.0.10 6.4.0.11 6.4.0.12 6.4.0.13 6.4.0.14 6.4.0.15 6.4.0.16 6.4.0.17 6.4.0.18 6.4.0.2 6.4.0.3 6.4.0.4 6.4.0.5 6.4.0.6 6.4.0.7 6.4.0.8 6.4.0.9 7.0.0 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 7.1.0 7.1.0.1 7.1.0.2 7.1.0.3 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 7.3.0 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 7.6.0 7.7.0

Affected range stops below 7.0.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 7.2.10, so it looks safe — our inference, not a vendor statement

Affected range stops below 7.4.3, so it looks safe — our inference, not a vendor statement

Affected range stops below 7.6.1, so it looks safe — our inference, not a vendor statement

Affected range stops below 7.7.10, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-SpOFF2Re

References (1)

Vendor Advisory

Source: cverecord

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-SpOFF2Re

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.6HIGHcisco

Attack Vector: NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: CHANGED
Confidentiality: NONE
Integrity: NONE
Availability: HIGH

Vector?

Quick Info

StatusANALYZED

CWE

CWE-244

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