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Vulnerabilities

Vulnerability · CVE-2026-20021

A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could…

Published Mar 4, 2026 · catalog updated Aug 11, 2026 · adaptive security appliance software

Check if you run it

No confirmed exploitation is on record for CVE-2026-20021. EPSS is 0.21%. Act only if a listed version of adaptive security appliance software is installed.

Severity
Medium4.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.21%
Remediation
Advisory link
Affected products
cpe cisco/adaptive security appliance software · cpe cisco/secure firewall threat defense

A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, adjacent attacker to exhaust memory on an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to improperly validating input by the OSPF protocol when parsing packets. An attacker could exploit this vulnerability by by sending crafted OSPF packets to an affected device. A successful exploit could allow the attacker to exhaust memory on the affected device, resulting in a DoS condition.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe cisco/adaptive security appliance softwareversion unspecified
  • cpe cisco/secure firewall threat defense6.4.0

How to fix CVE-2026-20021

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-20021. EPSS is 0.21%. Act only if a listed version of adaptive security appliance software is installed.

Which versions are affected?

Compare what you have installed with cisco/secure firewall threat defense 6.4.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-401: Missing Release of Memory after Effective Lifetime. EPSS 0.21%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Cisco security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 4, 2026 · NIST NVD

    Detected

    A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, adjacent attacker to exhaust memory on an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to improperly validating input by the OSPF protocol when parsing packets.

  2. Aug 11, 2026 · NIST NVD

    Updated

    A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, adjacent attacker to exhaust memory on an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to improperly validating input by the OSPF protocol when parsing packets.

Sources

  • CVE.orgVulnerability recordCVE-2026-20021

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-20021

    30-day exploitation probability 0.2%

    first.org
  • NIST NVDVulnerability recordCVE-2026-20021

    A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, adjacent attacker to exhaust memory on an affected device, resulting in a denial of servi

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.