What is CVE-2021-20090?

CVE-2021-20090 is a critical-severity vulnerability in Buffalo Wsr-2533dhp3-Bk, classified under Path Traversal. CVSS score: 9.8/10. Published 2021-04-29.

How severe is CVE-2021-20090?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-20090 known to be exploited?

Yes. CVE-2021-20090 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 17 public proof-of-concept repositories are indexed.

Path Traversal in Buffalo Wsr-2533dhp3-Bk

CVE-2021-20090

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.

Vulnerability class: Path Traversal (Directory Traversal)

Published 2021-04-29 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 1.000 (100.0th percentile), scored 2026-10-08.

Very high probability of exploitation in the next 30 days — among the top 0.1% most-likely-to-be-exploited CVEs. 100th percentile — 100.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 1.000 · newest: 1.000 · change: -0.000

Affected products

Buffalo Wsr-2533dhp3-Bk
Buffalo Wsr-2533dhp3-Bk Firmware
Buffalo Wsr-2533dhpl2-Bk
Buffalo Wsr-2533dhpl2-Bk Firmware
Buffalo Wsr-2533dhpl2, Wsr-2533dhp3 — versions WSR-2533DHPL2 <=1.02, WSR-2533DHP3 <= 1.24

Weakness classification (CWE)

CWE-22 — Path Traversal

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

www.tenable.com/security/research/tra-2021-13 (Exploit, Third Party Advisory)
www.kb.cert.org/vuls/id/914124 (US Government Resource, Third Party Advisory, third-party-advisory)
www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/ (Exploit, Third Party Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-20090?: CVE-2021-20090 is a critical-severity vulnerability in Buffalo Wsr-2533dhp3-Bk, classified under Path Traversal. CVSS score: 9.8/10. Published 2021-04-29.
How severe is CVE-2021-20090?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-20090 known to be exploited?: Yes. CVE-2021-20090 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 17 public proof-of-concept repositories are indexed.