# CVE-2021-36367: Auth bypass in n/a

> PuTTY allows malicious SSH servers to spoof authentication prompts, potentially capturing user credentials and leading to account takeover.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 9 Jul 2021
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2021-36367, DEBIAN-CVE-2021-36367, GHSA-wccm-6vx2-7p8c, UBUNTU-CVE-2021-36367

## What is CVE-2021-36367?

CVE-2021-36367 is a high-severity authentication bypass vulnerability in n/a, published on 9 Jul 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a substantive authentication response. This makes it easier for an attacker-controlled SSH server to present a later spoofed authentication prompt (that the attacker can use to capture credential data, and use that data for purposes that are undesired by the client user).

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2021-36367?

It affects 1 product.


Products: Putty Putty.

## How do I fix CVE-2021-36367?

Upgrade to a fixed version.

## Is CVE-2021-36367 being exploited?

There is no known exploitation of CVE-2021-36367 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2004-1008](https://insights.sbomify.com/CVE-2004-1008/): Integer overflow in n/a (critical 10.0)
- [CVE-2019-17067](https://insights.sbomify.com/CVE-2019-17067/): Other in n/a (critical 9.8)
- [CVE-2016-6167](https://insights.sbomify.com/CVE-2016-6167/): Other in n/a (high 7.8)
- [CVE-2021-33500](https://insights.sbomify.com/CVE-2021-33500/): Denial of service in n/a (high 7.5)
- [CVE-2005-0467](https://insights.sbomify.com/CVE-2005-0467/): Integer overflow in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36367 and fix it if it is affected.

What it is: CVE-2021-36367 is a high-severity authentication bypass vulnerability in n/a, published on 9 Jul 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-36367 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-2021-36367/ (Markdown: https://insights.sbomify.com/CVE-2021-36367/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36367
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36367
- OSV: https://osv.dev/vulnerability/CVE-2021-36367

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36367/
Summaries are generated and may contain mistakes; the official description above is the record.