Is CVE-2021-20090 in the CISA KEV catalog?

Yes. CVE-2021-20090 is on the CISA Known Exploited Vulnerabilities list, added 2021-11-03.

What is the CVSS severity of CVE-2021-20090?

CVE-2021-20090 has a CVSS v3 base score of 9.8 (CRITICAL).

What is the EPSS score for CVE-2021-20090?

CVE-2021-20090 has an EPSS score of 99.98% (100th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2021-20090?

No published fix for CVE-2021-20090 has been found yet. It is on the CISA Known Exploited Vulnerabilities list; federal agencies must remediate by 2021-11-17. Apply the vendor's mitigations per CISA's guidance.

CVE & CISA-KEV Catalog

CVE-2021-20090

CRITICALCISA KEVEPSS 100th pctl

9.8

CVSS v3

NVD

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.

CWE-22Path Traversal

How to fix

Actively exploited, no published fix found yet

CISA required action: Apply updates per vendor instructions.

Federal remediation due: 2021-11-17

Mitigation guidance may be in the linked vendor advisories in the References section below.

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CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

99.98%probability of exploitation in 30 days

100thpercentile

Very high risk: more likely to be exploited than 100% of all known CVEs.

Known Exploited Vulnerability (CISA KEV)

Arcadyan Buffalo Firmware Path Traversal Vulnerability

Arcadyan Buffalo firmware contains a path traversal vulnerability that could allow unauthenticated, remote attackers to bypass authentication and access sensitive information. This vulnerability affects multiple routers across several different vendors.

Apply updates per vendor instructions.

Remediation due: 2021-11-17

References

Exploit2

Third-Party Advisory1

kb.cert.org

Government Resource1

cisa.gov

Related Vulnerabilities

Other CWE-22 (Path Traversal) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-23897	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-32315	High	8.6	100%	KEV	Fix
CVE-2022-29464	Critical	9.8	100%	KEV + Ransom	-
CVE-2021-26086	Medium	5.3	100%	KEV	Fix
CVE-2021-22005	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2020-5902	Critical	9.8	100%	KEV + Ransom	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-03.