CVE-2020-3572: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SSL/TLS Session Denial of Service Vulnerability

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-10-21 · updated 2026-08-11
Weakness: CWE-400

Description

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 products

Cisco Adaptive Security Appliance: before 9.6 — fixed in 9.6
Cisco ASA Software: from 9.8.0 before 9.8.4.26; from 9.9.0 before 9.9.2.80; from 9.10.0 before 9.10.1.44; from 9.12.0 before 9.12.4.4; from 9.13.0 before 9.13.1.13; from 9.14.0 before 9.14.1.19 — fixed in 9.10.1.44, 9.12.4.4, 9.13.1.13, 9.14.1.19, 9.8.4.26, 9.9.2.80
Cisco Firepower Threat Defense Software: before 6.3.0.6; from 6.4.0 before 6.4.0.10; from 6.5.0 before 6.6.1 — fixed in 6.3.0.6, 6.4.0.10, 6.6.1

How to fix

Upgrade to a fixed version: Cisco Adaptive Security Appliance 9.6; Cisco ASA Software 9.10.1.44, 9.12.4.4, 9.13.1.13, 9.14.1.19; Cisco Firepower Threat Defense Software 6.3.0.6, 6.4.0.10, 6.6.1. Check the vendor advisory for mitigations.

References

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