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Vulnerabilities

Vulnerability · CVE-2024-20353

Cisco ASA and FTD Denial of Service Vulnerability

Published Apr 24, 2024 · catalog updated Aug 11, 2026 · Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD)

Patch now

CVE-2024-20353 is in the CISA known-exploited catalog, due May 1, 2024. Confirm Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Severity
High8.6
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
70.69%
Remediation
Remediation guidance
Affected products
cpe cisco/adaptive security appliance software · cpe cisco/secure firewall threat defense · vendor Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD)

A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could exploit this vulnerability by sending a crafted HTTP request to a targeted web server on a device. A successful exploit could allow the attacker to cause a DoS condition when the device reloads.

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 software9.8.1
  • cpe cisco/adaptive security appliance software9.8.1.5
  • cpe cisco/adaptive security appliance software9.8.1.7
  • cpe cisco/adaptive security appliance software9.8.2
  • cpe cisco/adaptive security appliance software9.8.2.14
  • cpe cisco/adaptive security appliance software9.8.2.15
  • cpe cisco/adaptive security appliance software9.8.2.17
  • cpe cisco/adaptive security appliance software9.8.2.8
  • cpe cisco/secure firewall threat defense6.2.3
  • vendor Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD)version unspecified

How to fix CVE-2024-20353

What to do

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

Should you patch?

CVE-2024-20353 is in the CISA known-exploited catalog, due May 1, 2024. Confirm Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with cisco/adaptive security appliance software 9.8.1; cisco/adaptive security appliance software 9.8.1.5; cisco/adaptive security appliance software 9.8.1.7; cisco/adaptive security appliance software 9.8.2. Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

What should an analyst verify?

CWE-835: Infinite Loop. EPSS 70.69%. The CISA KEV listing is the exploitation evidence. 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. Apr 24, 2024 · Catalog

    Detected

    A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could

  2. Apr 24, 2024 · CISA KEV

    Known exploited

    Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

  3. May 1, 2024 · CISA KEV

    Remediation due

    Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

  4. Aug 11, 2026 · Catalog

    Updated

    A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could

Sources

  • CERT-FRGovernment advisoryCVE-2024-20353

    Le 24 avril 2024, Cisco a publié trois avis de sécurité concernant des vulnérabilités affectant les équipements de sécurité ASA et FTD. Deux d'entre eux concernent les vulnérabilités CVE-2024-20353 et CVE-2024-20359 qui sont activement exploitées dans le cadre d'attaques ciblées.

    cert.ssi.gouv.fr
  • CISA KEVConfirmed exploitationCVE-2024-20353

    Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) contain an infinite loop vulnerability that can lead to remote denial of service condition.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2024-20353

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2024-20353

    30-day exploitation probability 70.7%

    first.org
  • NIST NVDVulnerability recordCVE-2024-20353

    A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of servic

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-2024-20353

    Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) contain an infinite loop vulnerability that can lead to remote denial of service condition.

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.