Update from October 22nd, 2020: Cisco has become aware of a new Cisco Adaptive Security Appliance vulnerability that could affect the fixed releases recommended for code trains 9.13 and 9.14 in the Fixed Software section of this advisory. See the Cisco Adaptive Security Appliance Software SSL/TLS Denial of Service Vulnerability for additional information.


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.

Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-tcp-dos-N3DMnU4T

This advisory is part of the October 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication, which includes 17 Cisco Security Advisories that describe 17 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: October 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Security Impact Rating: High

CVE: CVE-2020-3572

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