# CVE-2021-43666: Denial of service in n/a

> An attacker can cause a denial of service in mbed TLS by providing an empty password to the PKCS#12 derivation function.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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:** Yes
- **Published:** 24 Mar 2022
- **Updated:** 2 Dec 2025
- **Also known as:** DEBIAN-CVE-2021-43666, GHSA-cgwh-hfr7-38m2, JLSEC-2025-217, UBUNTU-CVE-2021-43666

## What is CVE-2021-43666?

CVE-2021-43666 is a high-severity denial of service vulnerability in Arm Mbed Tls, published on 24 Mar 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A Denial of Service vulnerability exists in mbed TLS 3.0.0 and earlier in the mbedtls_pkcs12_derivation function when an input password's length is 0.

Weakness: CWE-130 (Improper Handling of Length Parameter Inconsistency)

## Which versions are affected by CVE-2021-43666?

It affects 2 products.


Products: Arm Mbed Tls, Debian Debian Linux.

## How do I fix CVE-2021-43666?

Upgrade to a fixed version.

## Is CVE-2021-43666 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-43666 exists.

## Other vulnerabilities in Arm Mbed Tls

- [CVE-2026-34877](https://insights.sbomify.com/CVE-2026-34877/): Deserialization in n/a (critical 9.8)
- [CVE-2022-46393](https://insights.sbomify.com/CVE-2022-46393/): Memory corruption in n/a (critical 9.8)
- [CVE-2021-44732](https://insights.sbomify.com/CVE-2021-44732/): Use after free in n/a (critical 9.8)
- [CVE-2017-18187](https://insights.sbomify.com/CVE-2017-18187/): Integer overflow in n/a (critical 9.8)
- [CVE-2018-0487](https://insights.sbomify.com/CVE-2018-0487/): Memory corruption in ARM mbed TLS before 1.3.22, before 2.1.10, and before 2.7.0 (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43666 and fix it if it is affected.

What it is: CVE-2021-43666 is a high-severity denial of service vulnerability in Arm Mbed Tls, published on 24 Mar 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-43666 exists.

Affected product: Arm Mbed Tls. 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-2021-43666/ (Markdown: https://insights.sbomify.com/CVE-2021-43666/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43666
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43666
- OSV: https://osv.dev/vulnerability/CVE-2021-43666

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43666/
Summaries are generated and may contain mistakes; the official description above is the record.