High severity · published Mar 4, 2026
CVE-2026-20039
Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability
8.6
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 31% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CS
Cisco Secure Firewall Adaptive Security Appliance (ASA) Software · Cisco
9.12.3; 9.12.1; 9.12.2; 9.12.4; 9.12.3.2; 9.12.3.7; +34 more · source: vendor
CS
Cisco Secure Firewall Threat Defense (FTD) Software · Cisco
6.4.0.1; 6.4.0.2; 6.4.0.5; 6.4.0; 6.4.0.3; 6.4.0.4; +34 more · source: vendor
AS
Adaptive Security Appliance Software · Cisco
9.12.1 before 9.16.4.84; 9.17.1 before 9.18.4.57; 9.19.1 before 9.20.3.16; 9.22.1.1 before 9.22.2.4; 9.23.1 before 9.23.1.3 · source: NVD
SF
Secure Firewall Threat Defense · Cisco
6.4.0 before 7.0.9; 7.1.0 before 7.2.10; 7.3.0 before 7.4.3; 7.6.0 before 7.6.1; 7.7.0 before 7.7.10 · source: NVD
Affected product
CS
Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
Cisco
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