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Bhr 4rv FirmwareOperating system · Buffalo

CVE-2021-20716

CRITICAL · 9.8 CVSS v3.1 Published 2021-04-28
Fix available
A fix is available. Upgrade to after 2.55 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Hidden functionality in multiple Buffalo network devices (BHR-4RV firmware Ver.2.55 and prior, FS-G54 firmware Ver.2.04 and prior, WBR2-B11 firmware Ver.2.32 and prior, WBR2-G54 firmware Ver.2.32 and prior, WBR2-G54-KD firmware Ver.2.32 and prior, WBR-B11 firmware Ver.2.23 and prior, WBR-G54 firmware Ver.2.23 and prior, WBR-G54L firmware Ver.2.20 and prior, WHR2-A54G54 firmware Ver.2.25 and prior, WHR2-G54 firmware Ver.2.23 and prior, WHR2-G54V firmware Ver.2.55 and prior, WHR3-AG54 firmware Ver.2.23 and prior, WHR-G54 firmware Ver.2.16 and prior, WHR-G54-NF firmware Ver.2.10 and prior, WLA2-G54 firmware Ver.2.24 and prior, WLA2-G54C firmware Ver.2.24 and prior, WLA-B11 firmware Ver.2.20 and prior, WLA-G54 firmware Ver.2.20 and prior, WLA-G54C firmware Ver.2.20 and prior, WLAH-A54G54 firmware Ver.2.54 and prior, WLAH-AM54G54 firmware Ver.2.54 and prior, WLAH-G54 firmware Ver.2.54 and prior, WLI2-TX1-AG54 firmware Ver.2.53 and prior, WLI2-TX1-AMG54 firmware Ver.2.53 and prior, WLI2-TX1-G54 firmware Ver.2.20 and prior, WLI3-TX1-AMG54 firmware Ver.2.53 and prior, WLI3-TX1-G54 firmware Ver.2.53 and prior, WLI-T1-B11 firmware Ver.2.20 and prior, WLI-TX1-G54 firmware Ver.2.20 and prior, WVR-G54-NF firmware Ver.2.02 and prior, WZR-G108 firmware Ver.2.41 and prior, WZR-G54 firmware Ver.2.41 and prior, WZR-HP-G54 firmware Ver.2.41 and prior, WZR-RS-G54 firmware Ver.2.55 and prior, and WZR-RS-G54HP firmware Ver.2.55 and prior) allows a remote attacker to enable the debug option and to execute arbitrary code or OS commands, change the configuration, and cause a denial of service (DoS) condition.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Multiple Buffalo network device firmware versions contain undocumented hidden/debug functionality that allows a remote unauthenticated attacker to enable debug mode, execute arbitrary OS commands, modify device configuration, or cause denial of service. This is effectively an undocumented backdoor accessible without authentication.

MitigationUpdate affected Buffalo router and access point firmware to versions beyond those specified in the advisory. If patches are unavailable for older devices, consider replacing them with supported hardware and implement network segmentation to limit exposure to untrusted networks.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Bhr 4rv FirmwareOperating system
Affected:<= 2.55
Fs G54 FirmwareOperating system
Affected:<= 2.04
Wbr2 B11 FirmwareOperating system
Affected:<= 2.32
Wbr2 G54 FirmwareOperating system
Affected:<= 2.32
Wbr2 G54 Kd FirmwareOperating system
Affected:<= 2.32
Wbr B11 FirmwareOperating system
Affected:<= 2.23
Wbr G54 FirmwareOperating system
Affected:<= 2.23
Wbr G54l FirmwareOperating system
Affected:<= 2.20

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Buffalo device model
    Access the device's web administration interface, check the product label, or use network discovery tools to determine the exact Buffalo model number (Bhr 4rv, Fs G54, Wbr2 B11, Wbr2 G54, Wbr2 G54 Kd, Wbr B11, Wbr G54, or Wbr G54l)
    Affected if The device is any of these Buffalo models: Bhr 4rv, Fs G54, Wbr2 B11, Wbr2 G54, Wbr2 G54 Kd, Wbr B11, Wbr G54, or Wbr G54l
  2. Check installed firmware version
    Log into the device's web interface (typically via http://192.168.1.1 or similar) and navigate to the Status or System Information page to view the firmware version, or use the command line if telnet/ssh access is available
    Affected if The installed firmware version is at or below 2.55 for Bhr 4rv, 2.04 for Fs G54, 2.32 for Wbr2 models, 2.23 for Wbr B11/G54, or 2.20 for Wbr G54l
  3. Inspect for undocumented debug interfaces
    Examine the device's web interface for hidden pages, debug menus, or diagnostic functions not documented in the user manual. Check for unusual URLs or parameters that may trigger debug mode. Review HTTP responses for hidden parameters or debug flags.
    Affected if Hidden debug interfaces, undocumented diagnostic pages, or debug mode parameters are present and accessible without authentication

A user is affected if they operate any of the listed Buffalo router or access point models running firmware at or below the specified version limits, as these contain an unauthenticated backdoor that allows debug mode activation and arbitrary command execution.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to a release after 2.55
Interim mitigation

Update affected Buffalo router and access point firmware to versions beyond those specified in the advisory. If patches are unavailable for older devices, consider replacing them with supported hardware and implement network segmentation to limit exposure to untrusted networks.

Fix this in Bhr 4rv Firmware Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20716 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data