CVE-2026-20154: Cisco Secure Firewall ASA/FTD denial of service in syslog rate limiting

CVE-2026-20154 · Severity: high · CVSS 8.6 · Published 2026-09-16

Cisco Secure Firewall ASA and Threat Defense (FTD) devices can be remotely attacked without authentication by flooding TCP SYN packets, which triggers excessive logging and consumes CPU resources. When syslog is enabled (the default configuration), this attack causes the device to become unresponsive, disrupting network traffic and security services that protect the organization's perimeter.

Technologies: Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Secure Firewall Threat Defense (FTD) Software. Vendors: Cisco.

Quick answers

Is CVE-2026-20154 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-20154 being exploited in the wild.
How severe is CVE-2026-20154?
High severity, with a CVSS score of 8.6, published 16 September 2026.
Which products and versions are affected?
Cisco Secure Firewall Adaptive Security Appliance (ASA) Software; Cisco Secure Firewall Threat Defense (FTD) Software.
Is there a fix for CVE-2026-20154?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-20154 attacked?
It is attacked over the network.
Am I affected by CVE-2026-20154?
Check whether you run Cisco Secure Firewall Adaptive Security Appliance (ASA) Software or Cisco Secure Firewall Threat Defense (FTD) Software. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

This vulnerability (CWE-835: Infinite Loop) stems from improper rate limiting of syslog message 419002 in Cisco Secure Firewall ASA and FTD software. An unauthenticated remote attacker can exploit this by sending a flood of TCP SYN packets to an affected device. The attack vector is network-based with no prerequisites, as the vulnerability is triggered when syslog logging is globally enabled (default configuration) and message 419002 is at an active logging level. A successful exploit causes high CPU utilization and performance degradation, resulting in denial of service. Cisco has released software updates and identified workarounds to mitigate the vulnerability.

Affected products

  • Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
  • Cisco Secure Firewall Threat Defense (FTD) Software

Timeline

  • 2026-09-16: disclosed: Vulnerability publicly disclosed by Cisco Security Advisory cisco-sa-asa-ftd-logging-dos-ZXXNesfN
  • 2026-09-18: other: Advisory updated with final information

References

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