CVE-2021-20647
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 · uneditedCross-site request forgery (CSRF) vulnerability in ELECOM WRC-300FEBK-S allows remote attackers to hijack the authentication of administrators and execute an arbitrary request via unspecified vector. As a result, the device settings may be altered and/or telnet daemon may be started.
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 · moderate confidenceCross-site request forgery (CSRF) vulnerability in ELECOM WRC-300FEBK-S router allows remote attackers to trick authenticated administrators into executing unintended requests by tricking their browsers. The vulnerability enables attackers to modify device settings and activate the telnet daemon, potentially exposing the device to further attacks.
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 dataall versionsCVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Confirm device modelAccess the router admin interface and navigate to the status or system information page to verify the exact model number is Elecom WRC-300FEBK-SAffected if The device is an Elecom WRC-300FEBK-S router
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Check firmware versionIn the router admin panel, locate the firmware version information typically found under Administration, System, or Status sectionsAffected if The firmware version is any version (all versions are affected)
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Verify CSRF token presence in admin formsLog into the router web interface, inspect the HTML source of configuration forms (such as network settings or admin password pages), and check whether each form includes a unique anti-CSRF token or nonce fieldAffected if Forms lack anti-CSRF tokens or use predictable/constant token values
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Test Referer header validationSubmit a configuration change request from an external source or without a valid Referer header and observe whether the router accepts or rejects the requestAffected if The router accepts requests without validating the Referer header or origin
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Check for telnet service activation capabilityIn the router admin interface, look for settings related to remote management, services, or telnet/SSH access; determine whether these settings can be modified via the web interfaceAffected if Telnet service can be enabled through the web admin panel without additional authentication barriers
If the device is an Elecom WRC-300FEBK-S and its web admin forms lack anti-CSRF token protection, the environment is affected by this vulnerability.
Generated from the published advisory. Verify against your own configuration.
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 dataApply vendor-supplied firmware update when available; until then, avoid accessing the router admin interface from untrusted networks and enable any available CSRF protections in the device settings.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20647 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-20647 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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