---
title: "CVE-2024-20353: Cisco ASA and FTD Denial of Service Vulnerability"
url: https://erroneo.us/security/cve/CVE-2024-20353/
description: "CVE-2024-20353 (Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD)): Exploited in the wild (CISA KEV). A vulnerability in the…"
type: vulnerability-record
section: "Security Digest"
date_published: 2024-04-24
date_modified: 2025-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2024-20353"
kev: true
cvss: 8.6
epss: 0.70686
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2024-20353: Cisco ASA and FTD Denial of Service Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD). CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2024-04-24, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2024-05-01 ; treat that as the outer limit, not the target.
- EPSS 70.7% , percentile 99: FIRST’s model estimates a 70.7% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

## What it is

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.

## Affected products (CVE record)

- Cisco Cisco Adaptive Security Appliance (ASA) Software: 9.8.1, 9.8.1.5, 9.8.1.7, 9.8.2, 9.8.2.8, 9.8.2.14, 9.8.2.15, 9.8.2.17, 9.8.2.20, 9.8.2.24, 9.8.2.26, 9.8.2.28
- Cisco Cisco Firepower Threat Defense Software: 6.2.3, 6.2.3.1, 6.2.3.2, 6.2.3.3, 6.2.3.4, 6.2.3.5, 6.2.3.6, 6.2.3.7, 6.2.3.8, 6.2.3.10, 6.2.3.11, 6.2.3.9

## Severity

- cisco CVSS 3.1: 8.6 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`

## Exploitation

- CISA KEV: added 2024-04-24; federal due date 2024-05-01. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 70.69% probability of exploitation activity in the next 30 days; percentile 99.

## Sources

- [Listed in CISA KEV notes (sec.cloudapps.cisco.com)](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2)
- [CVE.org record CVE-2024-20353](https://www.cve.org/CVERecord?id=CVE-2024-20353)
- [NVD entry CVE-2024-20353](https://nvd.nist.gov/vuln/detail/CVE-2024-20353)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-20353)
- [blog.talosintelligence.com](https://blog.talosintelligence.com/arcanedoor-new-espionage-focused-campaign-found-targeting-perimeter-network-devices/)

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Source page: https://erroneo.us/security/cve/CVE-2024-20353/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt