# CVE-2020-36421: Information disclosure in n/a

> A side-channel vulnerability in Mbed TLS allows attackers to disclose RSA private keys used in secure enclaves.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2021
- **Updated:** 3 Dec 2025
- **Also known as:** DEBIAN-CVE-2020-36421, GHSA-4h9j-8g4q-fcfq, JLSEC-2025-204, UBUNTU-CVE-2020-36421

## What is CVE-2020-36421?

CVE-2020-36421 is a medium-severity vulnerability in Arm Mbed Tls, published on 19 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Arm Mbed TLS before 2.23.0. Because of a side channel in modular exponentiation, an RSA private key used in a secure enclave could be disclosed.

Weakness: CWE-203 (Observable Discrepancy)

## Which versions are affected by CVE-2020-36421?

It affects 2 products.


Products: Arm Mbed Tls, Debian Debian Linux.

## How do I fix CVE-2020-36421?

Upgrade to a fixed version.

## Is CVE-2020-36421 being exploited?

There is no known exploitation of CVE-2020-36421 in the wild and no public exploit code.

## 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-2020-36421 and fix it if it is affected.

What it is: CVE-2020-36421 is a medium-severity vulnerability in Arm Mbed Tls, published on 19 Jul 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-2020-36421 in the wild and no public exploit code.

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-2020-36421/ (Markdown: https://insights.sbomify.com/CVE-2020-36421/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-36421
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-36421
- OSV: https://osv.dev/vulnerability/CVE-2020-36421

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-36421/
Summaries are generated and may contain mistakes; the official description above is the record.