# CVE-2021-36369: Auth bypass in n/a

> A non-RFC-compliant authentication check in Dropbear allows attackers to bypass security measures like FIDO2 tokens and abuse forwarded agents for unauthorized access.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/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:** 12 Oct 2022
- **Updated:** 15 May 2025
- **Also known as:** DEBIAN-CVE-2021-36369, DLA-3187-1, GHSA-mwx5-864v-x3jc, MGASA-2022-0436, UBUNTU-CVE-2021-36369

## What is CVE-2021-36369?

CVE-2021-36369 is a high-severity authentication bypass vulnerability in Debian Debian Linux, published on 12 Oct 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attack can bypass additional security measures such as FIDO2 tokens or SSH-Askpass. Thus, it allows an attacker to abuse a forwarded agent for logging on to another server unnoticed.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-36369?

It affects 2 products.


Products: Debian Debian Linux, Dropbear Ssh Project Dropbear Ssh.

## How do I fix CVE-2021-36369?

Apply the vendor's patch.

## Is CVE-2021-36369 being exploited?

There is no known exploitation of CVE-2021-36369 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36369 and fix it if it is affected.

What it is: CVE-2021-36369 is a high-severity authentication bypass vulnerability in Debian Debian Linux, published on 12 Oct 2022. 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-2021-36369 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-36369/ (Markdown: https://insights.sbomify.com/CVE-2021-36369/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36369
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36369
- OSV: https://osv.dev/vulnerability/CVE-2021-36369

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36369/
Summaries are generated and may contain mistakes; the official description above is the record.