Denial of Service Vulnerability in Cisco Secure Firewall Products
CVE-2026-20039

8.6HIGH

Key Information:

Vendor

Cisco
Status
Cisco Secure Firewall Adaptive Security Appliance (asa) Software
Cisco Secure Firewall Threat Defense (ftd) Software
Vendor
CVE Published:
4 March 2026

Badges

👾 Exploit Exists

What is CVE-2026-20039?

A vulnerability exists in the VPN web server of Cisco's Secure Firewall Adaptive Security Appliance and Threat Defense Software. This issue arises from improper memory management, enabling unauthenticated remote attackers to overwhelm the device by sending a barrage of specially crafted HTTP requests. If successfully exploited, this could lead to the affected device reloading unexpectedly, thereby creating a denial of service condition.

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Affected Version(s)

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.3

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.1

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12.2

References

https://sec.cloudapps.cisco.com/security/center/content/C...

CVSS V3.1

Score:
8.6
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Changed

Timeline

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

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