Security readout for executives and security teams
Plain-English summary
This flaw lets an unauthenticated remote attacker bypass authentication on affected Buffalo router web interfaces by abusing path traversal. For leadership, the concern is exposed edge devices: if reachable, attackers may gain high-impact access without credentials. CISA KEV indicates known exploitation.
Executive priority
Treat this as urgent for exposed or unmanaged edge devices. The combination of no-auth remote attack potential, critical CVSS, and KEV listing makes rapid inventory, isolation, and vendor-guided remediation appropriate.
Technical view
CVE-2021-20090 is a CWE-22 path traversal issue in Buffalo WSR-2533DHPL2 firmware <=1.02 and WSR-2533DHP3 firmware <=1.24. It is network reachable, low complexity, requires no privileges or user interaction, and carries CVSS 3.1 score 9.8 with high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most likely where affected Buffalo router web administration interfaces are reachable from untrusted networks. Internet-facing or poorly segmented edge devices are the highest concern. Internal-only management interfaces still matter if attackers gain a network foothold.
Exploitation context
CISA lists CVE-2021-20090 in KEV, supporting known exploited status. The bundle also cites reporting on active exploitation of Arcadyan-based routers and modems. The provided evidence does not include exploit volumes, specific campaigns, or proof that every affected Buffalo deployment is targeted.
Researcher notes
The source bundle establishes the vulnerable models, firmware thresholds, CWE-22 classification, CVSS vector, and KEV status. It does not provide complete exploit telemetry, full downstream vendor scope, or a detailed fix matrix, so avoid broad product claims beyond cited sources.
Mitigation direction
- Identify Buffalo WSR-2533DHPL2 and WSR-2533DHP3 devices and confirm firmware versions.
- Apply Buffalo or vendor firmware guidance for versions affected by this CVE.
- Disable internet exposure of router web administration interfaces wherever possible.
- Restrict management access to trusted administrative networks only.
- Replace unsupported devices if no vendor-fixed firmware is available.
Validation and detection
- Inventory perimeter and branch routers for the named Buffalo models.
- Check firmware against WSR-2533DHPL2 <=1.02 and WSR-2533DHP3 <=1.24.
- Review external attack surface for exposed web administration interfaces.
- Confirm remediation by documenting updated firmware or compensating access restrictions.
- Monitor vendor, CISA KEV, and CERT guidance for any updated scope.
Public sources used
Michael Williams reviewed this cited source version on .
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-22: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-20090 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.tenable.com/security/research/tra-2021-13CVE reference
- VU#914124CVE reference · third-party-advisory
- https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/CVE reference
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20090CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.