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

> Unauthenticated remote attackers can cause Cisco ASA and FTD devices to reload unexpectedly via crafted HTTP requests, resulting in a denial of service.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Yes, since 24 Apr 2024 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Apr 2024
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-pp78-fggv-r899

## What is CVE-2024-20353?

CVE-2024-20353 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 24 Apr 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2024-20353?

It affects 2 products.


Products: Cisco Adaptive Security Appliance Software, Cisco Secure Firewall Threat Defense.

## How do I fix CVE-2024-20353?

No fix has been published for CVE-2024-20353 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 1 May 2024.

## Is CVE-2024-20353 being exploited?

Yes. Attackers have exploited CVE-2024-20353 in the wild since at least 24 Apr 2024.

## Other vulnerabilities in Cisco Adaptive Security Appliance Software

- [CVE-2025-20333](https://insights.sbomify.com/CVE-2025-20333/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow (critical 9.9, exploited in the wild)
- [CVE-2016-6366](https://insights.sbomify.com/CVE-2016-6366/): Cisco Adaptive Security Appliance (ASA) SNMP Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2026-20349](https://insights.sbomify.com/CVE-2026-20349/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection (high 8.6, exploited in the wild)
- [CVE-2016-6367](https://insights.sbomify.com/CVE-2016-6367/): Cisco Adaptive Security Appliance (ASA) CLI Remote Code Execution (high 7.8, exploited in the wild)
- [CVE-2020-3452](https://insights.sbomify.com/CVE-2020-3452/): Cisco ASA and FTD Read-Only Path Traversal (high 7.5, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-20353 and fix it if it is affected.

What it is: CVE-2024-20353 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 24 Apr 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2024-20353 in the wild since at least 24 Apr 2024.

Affected product: Cisco Adaptive Security Appliance Software. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-20353/ (Markdown: https://insights.sbomify.com/CVE-2024-20353/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-20353
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-20353
- OSV: https://osv.dev/vulnerability/CVE-2024-20353

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From sbomify Insights: https://insights.sbomify.com/CVE-2024-20353/
Summaries are generated and may contain mistakes; the official description above is the record.