---
id: CVE-2020-3572
title: >-
  A vulnerability in the SSL/TLS session handler of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to cause a denial of service
  (DoS) condi…
summary: >-
  A vulnerability in the SSL/TLS session handler of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to cause a denial of service
  (DoS) condi…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-401
vendor: cisco
product: adaptive_security_appliance
affected:
  - adaptive_security_appliance < 9.6
  - secure_firewall_threat_defense < 6.3.0.6
  - 'secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10'
  - 'secure_firewall_threat_defense >= 6.5.0, < 6.6.1'
  - 'adaptive_security_appliance_software >= 9.8.0, < 9.8.4.26'
  - 'adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80'
  - 'adaptive_security_appliance_software >= 9.10.0, < 9.10.1.44'
  - 'adaptive_security_appliance_software >= 9.12.0, < 9.12.4.4'
  - 'adaptive_security_appliance_software >= 9.13.0, < 9.13.1.13'
  - 'adaptive_security_appliance_software >= 9.14.0, < 9.14.1.19'
patched:
  - adaptive_security_appliance 9.6
  - secure_firewall_threat_defense 6.6.1
  - adaptive_security_appliance_software 9.14.1.19
published: '2020-10-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3572'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-tcp-dos-N3DMnU4T
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-tcp-dos-N3DMnU4T
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01778
epssPercentile: 0.7728
ingestedAt: '2026-08-18T12:28:06.425Z'
---

## Overview

A vulnerability in the SSL/TLS session handler of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a memory leak when closing SSL/TLS connections in a specific state. An attacker could exploit this vulnerability by establishing several SSL/TLS sessions and ensuring they are closed under certain conditions. A successful exploit could allow the attacker to exhaust memory resources in the affected device, which would prevent it from processing new SSL/TLS connections, resulting in a DoS. Manual intervention is required to recover an affected device.

## Affected

- `adaptive_security_appliance < 9.6`
- `secure_firewall_threat_defense < 6.3.0.6`
- `secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10`
- `secure_firewall_threat_defense >= 6.5.0, < 6.6.1`
- `adaptive_security_appliance_software >= 9.8.0, < 9.8.4.26`
- `adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80`
- `adaptive_security_appliance_software >= 9.10.0, < 9.10.1.44`
- `adaptive_security_appliance_software >= 9.12.0, < 9.12.4.4`
- `adaptive_security_appliance_software >= 9.13.0, < 9.13.1.13`
- `adaptive_security_appliance_software >= 9.14.0, < 9.14.1.19`

## Remediation

Upgrade past the affected range:

- `adaptive_security_appliance 9.6`
- `secure_firewall_threat_defense 6.6.1`
- `adaptive_security_appliance_software 9.14.1.19`