CVE-2026-20039 | Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability

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.

Published: 2026-03-04 Last update: 2026-04-16 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-20039 is rated Moderate Risk (43.4/100): CVSS High severity, with low exploitation likelihood (EPSS 0.09%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-20039

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-17 0.15% 0.09% -0.06%
2 2026-03-10 0.12% 0.15% +0.04%
3 2026-03-05 — 0.12% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-20039

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.6 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 4.0 [email protected]

Weakness enumeration for CVE-2026-20039

Affected software / configurations for CVE-2026-20039

Vendor Product Version Raw CPE
cisco adaptive_security_appliance_software >= 9.12.1, < 9.16.4.84 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.17.1, < 9.18.4.57 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.19.1, < 9.20.3.16 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.22.1.1, < 9.22.2.4 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco adaptive_security_appliance_software >= 9.23.1, < 9.23.1.3 cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cisco firepower_threat_defense_software >= 6.4.0, < 7.0.9 cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*
cisco firepower_threat_defense_software >= 7.1.0, < 7.2.10 cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*
cisco firepower_threat_defense_software >= 7.3.0, < 7.4.3 cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*
cisco firepower_threat_defense_software >= 7.6.0, < 7.6.1 cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*
cisco firepower_threat_defense_software >= 7.7.0, < 7.7.10 cpe:2.3:a:cisco:firepower_threat_defense_software:*:*:*:*:*:*:*:*

References for CVE-2026-20039

cvelogic Threat Intelligence