# CVE-2021-33500: Denial of service in n/a

> A remote server can cause a denial of service in PuTTY by rapidly changing the window title, leading to a GUI hang.

- **Severity:** High 7.5 (`CVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** CVE-2021-26940, GHSA-vmq2-m9cv-qwqx, UBUNTU-CVE-2021-33500

## What is CVE-2021-33500?

CVE-2021-33500 is a high-severity denial of service vulnerability in n/a, published on 21 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.

## Which versions are affected by CVE-2021-33500?

It affects 1 product.


Products: Putty Putty.

## How do I fix CVE-2021-33500?

No fix has been published for CVE-2021-33500 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-33500 being exploited?

There is no known exploitation of CVE-2021-33500 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-2021-36367](https://insights.sbomify.com/CVE-2021-36367/): Auth bypass in n/a (high 8.1)
- [CVE-2016-6167](https://insights.sbomify.com/CVE-2016-6167/): Other in n/a (high 7.8)
- [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-2021-33500 and fix it if it is affected.

What it is: CVE-2021-33500 is a high-severity denial of service vulnerability in n/a, published on 21 May 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-2021-33500 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-2021-33500/ (Markdown: https://insights.sbomify.com/CVE-2021-33500/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33500
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33500
- OSV: https://osv.dev/vulnerability/CVE-2021-33500

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33500/
Summaries are generated and may contain mistakes; the official description above is the record.