IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2021-20090|Auth: none — unauthenticated|Reboot: required|Manual only

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.

Published Apr 29, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2021-11-17 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Path Traversal (CWE-22) vulnerability in Arcadyan Buffalo Firmware. 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

🖼

Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

IT Security
Running wsr-2533dhpl2-bk firmware: v ≤ 1.02; wsr-2533dhp3-bk firmware: v ≤ 1.24
Real-world incidentsWhat we've seen

Active exploitation documented in the wild. Threat-research write-up: https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/

How to patch

Manual remediation steps

Apply the Vendor Patch

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.

CISA required action: Apply updates per vendor instructions.

References

    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-20090
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20090
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