← Vulnerability feed

Vulnerability record · CVE-2026-20039 · published 4 March 2026

CVE-2026-20039: Cisco adaptive security appliance software vulnerability

Cisco · Adaptive Security Appliance Software

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.

8.6 CVSS 3.1 High EPSS 0.36% · top 72.9% CWE-244 · CWE-244
8.6CVSS 3.1 base score
0.36%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
1References
11 Aug 2026Last modified by 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.

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

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

Track CVE-2026-20039 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2021-44228Apache Log4j2 JNDI lookup remote code executionApache Log4j2 versions 2.0-beta9 through 2.15.0 (excluding 2.12.2, 2.12.3, and 2.3.1) do not protect against attacker-controlled LDAP and other JNDI …KEVEPSS 100%analysed9.9CVE-2025-20333Cisco ASA and FTD VPN web server buffer overflow allows root RCECisco Secure Firewall ASA and FTD Software fail to properly validate user-supplied input in HTTP(S) requests to the VPN web server, causing a classic…KEVEPSS 71%analysed9.1CVE-2023-20269Cisco ASA and FTD remote access VPN AAA separation flawCisco ASA and FTD remote access VPN features fail to properly separate AAA from the HTTPS management and site-to-site VPN features. An attacker can s…KEVEPSS 25%analysed8.8CVE-2016-6366Cisco ASA SNMP buffer overflow allows remote code executionCisco ASA, PIX and FWSM software through 9.4.2.3 contains a classic buffer overflow (CWE-120) reachable through crafted IPv4 SNMP packets. A remote a…KEVEPSS 88%analysed8.6CVE-2026-20349Cisco ASA and FTD SSL VPN HTTP request handling denial of serviceCisco Secure Firewall ASA and FTD software fail to properly check errors when processing HTTP requests in the Remote Access SSL VPN service. An unaut…KEVEPSS 1.0%analysed8.6CVE-2025-20362Cisco Secure Firewall ASA/FTD VPN web server missing authorizationThe VPN web server in Cisco Secure Firewall ASA and FTD software fails to properly validate user-supplied input in HTTP(S) requests, allowing access …KEVEPSS 87%analysed8.6CVE-2024-20353Cisco ASA and FTD web server HTTP header parsing DoSCisco ASA and FTD management and VPN web servers fail to fully check errors when parsing an HTTP header, so a crafted request can crash and reload th…KEVEPSS 71%analysed7.8CVE-2016-6367Cisco ASA CLI command injection privilege escalationCisco ASA Software before 8.4(1) on ASA 5500, ASA 5500-X, PIX, and FWSM devices mishandles invalid CLI commands, allowing command injection (CWE-77).…KEVEPSS 23%analysed

Source: NIST National Vulnerability Database (record CVE-2026-20039), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.