# CVE-2021-40125: Denial of service in Cisco Adaptive Security Appliance (ASA) Software

> An authenticated remote attacker can cause a device reload by sending malformed IKEv2 messages, affecting Cisco ASA and FTD software.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Oct 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-cg2g-27wj-x8x6

## What is CVE-2021-40125?

CVE-2021-40125 is a medium-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 27 Oct 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability in the Internet Key Exchange Version 2 (IKEv2) implementation of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an authenticated, remote attacker to trigger a denial of service (DoS) condition on an affected device. This vulnerability is due to improper control of a resource. An attacker with the ability to spoof a trusted IKEv2 site-to-site VPN peer and in possession of valid IKEv2 credentials for that peer could exploit this vulnerability by sending malformed, authenticated IKEv2 messages to an affected device. A successful exploit could allow the attacker to trigger a reload of the device.

Weakness: CWE-400 (Uncontrolled Resource Consumption), CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-40125?

It affects 10 products.


Products: 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-2021-40125?

No fix has been published for CVE-2021-40125 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40125 being exploited?

There is no known exploitation of CVE-2021-40125 in the wild and no public exploit code.

## 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-2024-20353](https://insights.sbomify.com/CVE-2024-20353/): Cisco ASA and FTD Denial of Service (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)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40125 and fix it if it is affected.

What it is: CVE-2021-40125 is a medium-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 27 Oct 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-40125 in the wild and no public exploit code.

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-2021-40125/ (Markdown: https://insights.sbomify.com/CVE-2021-40125/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40125
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40125
- OSV: https://osv.dev/vulnerability/CVE-2021-40125

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40125/
Summaries are generated and may contain mistakes; the official description above is the record.