Is CVE-2026-20039 in the CISA KEV catalog?

No. CVE-2026-20039 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-20039?

CVE-2026-20039 has a CVSS v3 base score of 8.6 (HIGH).

What is the EPSS score for CVE-2026-20039?

CVE-2026-20039 has an EPSS score of 0.36% (28th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-20039?

Upgrade adaptive security appliance software to 9.23.1.3 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2026-20039

HIGH

8.6

CVSS v3

NVD

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.

CWE-244

How to fix

Remediation Available

adaptive security appliance softwareNVD

Affected:>= 9.23.1, < 9.23.1.3Fixed in:9.23.1.3CVE-2026-20039derived from NVD

firepower threat defense softwareNVD

Affected:>= 7.7.0, < 7.7.10Fixed in:7.7.10CVE-2026-20039derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeChanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Exploit Intelligence

0.36%probability of exploitation in 30 days

28thpercentile

Low risk: more likely to be exploited than 28% of all known CVEs.

References

Vendor Advisory1

sec.cloudapps.cisco.com

Related Vulnerabilities

Other CWE-244 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2022-20943	Medium	5.8	0.9%	-	Fix
CVE-2022-20922	Medium	5.8	0.8%	-	-
CVE-2023-20070	Medium	4.0	0.5%	-	-
CVE-2023-20177	Medium	4.0	0.5%	-	-
CVE-2025-5105	High	7.3	0.4%	-	-
CVE-2025-26305	High	8.2	0.4%	-	-

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-16.