Cisco Secure Firewall Adaptive Security Appliance Software Embryonic Connection Limit release of resource

Summaryinfo

A vulnerability has been found in Cisco Secure Firewall Adaptive Security Appliance Software 9.20.4.14 and classified as critical. Affected by this vulnerability is an unknown functionality of the component Embryonic Connection Limit Handler. This manipulation causes release of resource. The identification of this vulnerability is CVE-2026-20082. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in Cisco Secure Firewall Adaptive Security Appliance Software 9.20.4.14 and classified as critical. Affected by this vulnerability is an unknown part of the component Embryonic Connection Limit Handler. The manipulation with an unknown input leads to a release of resource vulnerability. The CWE definition for the vulnerability is CWE-772. The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed. As an impact it is known to affect availability. The summary by CVE is:

A vulnerability in the handling of the embryonic connection limits in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause incoming TCP SYN packets to be dropped incorrectly. This vulnerability is due to improper handling of new, incoming TCP connections that are destined to management or data interfaces when the device is under a TCP SYN flood attack. An attacker could exploit this vulnerability by sending a crafted stream of traffic to an affected device. A successful exploit could allow the attacker to prevent all incoming TCP connections to the device from being established, including remote management access, Remote Access VPN (RAVPN) connections, and all network protocols that are TCP-based. This results in a denial of service (DoS) condition for affected features.

It is possible to read the advisory at sec.cloudapps.cisco.com. This vulnerability is known as CVE-2026-20082 since 10/08/2025. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 05/05/2026). The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading eliminates this vulnerability.

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Productinfo

Type

• Firewall Software

Vendor

• Cisco

Name

• Secure Firewall Adaptive Security Appliance Software

Version

• 9.20.4.14

License

• commercial

Website

• Vendor: https://www.cisco.com/

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