# CVE-2021-20090: Arcadyan Buffalo Firmware Path Traversal

> Unauthenticated attackers can exploit a path traversal flaw in Buffalo router web interfaces to bypass authentication mechanisms.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Yes, since 3 Nov 2021 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Apr 2021
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-6466-44wr-c6vv

## What is CVE-2021-20090?

CVE-2021-20090 is a critical path traversal vulnerability in Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3, published on 29 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A path traversal vulnerability in the web interfaces of Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 could allow unauthenticated remote attackers to bypass authentication.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2021-20090?

It affects 2 products.


Products: Buffalo Wsr-2533dhp3-Bk Firmware, Buffalo Wsr-2533dhpl2-Bk Firmware.

## How do I fix CVE-2021-20090?

No fix has been published for CVE-2021-20090 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 17 Nov 2021.

## Is CVE-2021-20090 being exploited?

Yes. Attackers have exploited CVE-2021-20090 in the wild since at least 3 Nov 2021.

Public exploit code:

- Buffalo WSR-2533DHPL2 - Path Traversal (nuclei): http/cves/2021/CVE-2021-20090.yaml

## Other vulnerabilities in Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3

- [CVE-2021-20091](https://insights.sbomify.com/CVE-2021-20091/): Command injection in Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3 (high 8.8)
- [CVE-2021-20092](https://insights.sbomify.com/CVE-2021-20092/): Information disclosure in Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3 (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20090 and fix it if it is affected.

What it is: CVE-2021-20090 is a critical path traversal vulnerability in Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3, published on 29 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-20090 in the wild since at least 3 Nov 2021.

Affected product: Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3. 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-2021-20090/ (Markdown: https://insights.sbomify.com/CVE-2021-20090/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20090
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20090
- OSV: https://osv.dev/vulnerability/CVE-2021-20090

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-20090/
Summaries are generated and may contain mistakes; the official description above is the record.