# CVE-2021-40118: Denial of service in Cisco Adaptive Security Appliance (ASA) Software

> Unauthenticated remote attackers can cause a denial of service by sending malicious HTTPS requests to Cisco ASA or FTD devices.

- **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:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Oct 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-6c9f-g24c-wm5r

## What is CVE-2021-40118?

CVE-2021-40118 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance, published on 27 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a denial of service (DoS) condition. This vulnerability is due to improper input validation when parsing HTTPS requests. An attacker could exploit this vulnerability by sending a malicious HTTPS request to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

Weakness: CWE-787 (Out-of-bounds Write), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2021-40118?

It affects 11 products.


Products: Cisco Adaptive Security Appliance, Cisco Adaptive Security Appliance Software, Cisco Asa 5505 Firmware, Cisco Asa 5512-X Firmware, Cisco Asa 5515-X Firmware, Cisco Asa 5525-X Firmware, Cisco Asa 5545-X Firmware, Cisco Asa 5555-X Firmware, Cisco Asa 5580 Firmware, Cisco Asa 5585-X Firmware, Cisco Secure Firewall Threat Defense.

## How do I fix CVE-2021-40118?

No fix has been published for CVE-2021-40118 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40118 being exploited?

There is no known exploitation of CVE-2021-40118 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Adaptive Security Appliance

- [CVE-2021-1573](https://insights.sbomify.com/CVE-2021-1573/): Denial of service in Cisco Adaptive Security Appliance Software (high 8.6)
- [CVE-2021-34793](https://insights.sbomify.com/CVE-2021-34793/): Denial of service in Cisco Adaptive Security Appliance (ASA) Software (high 8.6)
- [CVE-2021-40117](https://insights.sbomify.com/CVE-2021-40117/): Denial of service in Cisco Adaptive Security Appliance (ASA) Software (high 8.6)
- [CVE-2020-3304](https://insights.sbomify.com/CVE-2020-3304/): Denial of service in Cisco Adaptive Security Appliance (ASA) Software (high 8.6)
- [CVE-2020-3436](https://insights.sbomify.com/CVE-2020-3436/): File upload in Cisco Adaptive Security Appliance (ASA) Software (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40118 and fix it if it is affected.

What it is: CVE-2021-40118 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance, published on 27 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-40118 in the wild and no public exploit code.

Affected product: Cisco Adaptive Security Appliance. 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-2021-40118/ (Markdown: https://insights.sbomify.com/CVE-2021-40118/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40118
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40118
- OSV: https://osv.dev/vulnerability/CVE-2021-40118

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-40118/
Summaries are generated and may contain mistakes; the official description above is the record.