# CVE-2020-36477: Security feature bypass in n/a

> Attackers can bypass X.509 certificate validation by exploiting improper SubjectAltName type checking, allowing impersonation of domains via IP address certificates.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/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:** 23 Aug 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-36477, GHSA-qfcq-wvh3-6p75, JLSEC-2025-212, UBUNTU-CVE-2020-36477

## What is CVE-2020-36477?

CVE-2020-36477 is a medium-severity vulnerability in Arm Mbed Tls, published on 23 Aug 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 Mbed TLS before 2.24.0. The verification of X.509 certificates when matching the expected common name (the cn argument of mbedtls_x509_crt_verify) with the actual certificate name is mishandled: when the subjecAltName extension is present, the expected name is compared to any name in that extension regardless of its type. This means that an attacker could impersonate a 4-byte or 16-byte domain by getting a certificate for the corresponding IPv4 or IPv6 address (this would require the attacker to control that IP address, though).

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2020-36477?

It affects 1 product.


Products: Arm Mbed Tls.

## How do I fix CVE-2020-36477?

Upgrade to a fixed version.

## Is CVE-2020-36477 being exploited?

There is no known exploitation of CVE-2020-36477 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-2020-36477 and fix it if it is affected.

What it is: CVE-2020-36477 is a medium-severity vulnerability in Arm Mbed Tls, published on 23 Aug 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-2020-36477 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-2020-36477/ (Markdown: https://insights.sbomify.com/CVE-2020-36477/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-36477
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-36477
- OSV: https://osv.dev/vulnerability/CVE-2020-36477

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-36477/
Summaries are generated and may contain mistakes; the official description above is the record.