# CVE-2021-36371: Auth bypass in n/a

> Attackers can bypass mTLS client certificate requirements on protected backends by manipulating SNI and Host headers in specific multi-TLSContext configurations.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jul 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-hc2q-w3c3-348m

## What is CVE-2021-36371?

CVE-2021-36371 is a low-severity authentication bypass vulnerability in n/a, published on 9 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Emissary-Ingress (formerly Ambassador API Gateway) through 1.13.9 allows attackers to bypass client certificate requirements (i.e., mTLS cert_required) on backend upstreams when more than one TLSContext is defined and at least one configuration exists that does not require client certificate authentication. The attacker must send an SNI specifying an unprotected backend and an HTTP Host header specifying a protected backend. (2.x versions are unaffected. 1.x versions are unaffected with certain configuration settings involving prune_unreachable_routes and a wildcard Host resource.)

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2021-36371?

It affects 1 product.


Products: Getambassador Emissary-Ingress.

## How do I fix CVE-2021-36371?

No fix has been published for CVE-2021-36371 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-36371 being exploited?

There is no known exploitation of CVE-2021-36371 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36371 and fix it if it is affected.

What it is: CVE-2021-36371 is a low-severity authentication bypass vulnerability in n/a, published on 9 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-2021-36371 in the wild and no public exploit code.

Affected product: n/a. 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-2021-36371/ (Markdown: https://insights.sbomify.com/CVE-2021-36371/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36371
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36371
- OSV: https://osv.dev/vulnerability/CVE-2021-36371

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36371/
Summaries are generated and may contain mistakes; the official description above is the record.