How severe is CVE-2026-20039?

CVE-2026-20039 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-20039 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-20039?

CVE-2026-20039 primarily affects Cisco Adaptive Security Appliance Software. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-20039?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-20039 have an EU (EUVD) identifier?

Yes. CVE-2026-20039 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-9434.

When was CVE-2026-20039 published?

CVE-2026-20039 was published on 2026-03-04 and last updated on 2026-06-17.

CVE-2026-20039

CVE-2026-20039 is a high-severity vulnerability in Cisco Adaptive Security Appliance Software with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-244.

Key facts

Severity: High (CVSS 3.x base score 8.6)
EPSS exploit prediction: 0% (28th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-9434
Weakness: CWE-244
Affected product: Cisco Adaptive Security Appliance Software
Published: 2026-03-04
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-20039?: 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.
How severe is CVE-2026-20039?: CVE-2026-20039 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-20039 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-20039?: CVE-2026-20039 primarily affects Cisco Adaptive Security Appliance Software. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-20039?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-20039 have an EU (EUVD) identifier?: Yes. CVE-2026-20039 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-9434.
When was CVE-2026-20039 published?: CVE-2026-20039 was published on 2026-03-04 and last updated on 2026-06-17.

References

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

Affected products (2)

cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*

More vulnerabilities in Cisco Adaptive Security Appliance Software

CVE-2018-0101 — Critical (CVSS 10.0): A vulnerability in the Secure Sockets Layer (SSL) VPN functionality of the Cisco Adaptive Security Appliance (ASA)…
CVE-2013-5511 — Critical (CVSS 10.0): The Adaptive Security Device Management (ASDM) remote-management feature in Cisco Adaptive Security Appliance (ASA)…
CVE-2013-5509 — Critical (CVSS 10.0): The SSL implementation in Cisco Adaptive Security Appliance (ASA) Software 9.0 before 9.0(2.6) and 9.1 before 9.1(2)…
CVE-2007-2462 — Critical (CVSS 10.0): Unspecified vulnerability in Cisco Adaptive Security Appliance (ASA) and PIX 7.2 before 7.2(2)8, when using Layer 2…
CVE-2025-20333 — Critical (CVSS 9.9): A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco…
CVE-2024-20329 — Critical (CVSS 9.9): A vulnerability in the SSH subsystem of Cisco Adaptive Security Appliance (ASA) Software could allow an authenticated,…

All CVEs affecting Cisco Adaptive Security Appliance Software →

Other CWE-244 vulnerabilities

CVE-2025-26305 — High (CVSS 8.2): A memory leak has been identified in the parseSWF_SOUNDINFO function in util/parser.c of libming v0.4.8, which allows…
CVE-2025-26304 — High (CVSS 8.2): A memory leak has been identified in the parseSWF_EXPORTASSETS function in util/parser.c of libming v0.4.8.
CVE-2025-70873 — High (CVSS 7.5): An information disclosure issue in the zipfileInflate function in the zipfile extension in SQLite v3.51.1 and earlier…
CVE-2025-36118 — High (CVSS 7.5): IBM Storage Virtualize 8.4, 8.5, 8.7, and 9.1 IKEv1 implementation allows remote attackers to obtain sensitive…
CVE-2025-5105 — High (CVSS 7.3): A vulnerability was found in TOZED ZLT W51 up to 1.4.2 and classified as critical. Affected by this issue is some…
CVE-2025-45663 — Medium (CVSS 6.5): An issue in NetSurf v3.11 causes the application to read uninitialized heap memory when creating a dom_event structure.

Browse all CWE-244 vulnerabilities →