CVE-2021-34203
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 · uneditedD-Link DIR-2640-US 1.01B04 is vulnerable to Incorrect Access Control. Router ac2600 (dir-2640-us), when setting PPPoE, will start quagga process in the way of whole network monitoring, and this function uses the original default password and port. An attacker can easily use telnet to log in, modify routing information, monitor the traffic of all devices under the router, hijack DNS and phishing attacks. In addition, this interface is likely to be questioned by customers as a backdoor, because the interface should not be exposed.
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 confidenceThe D-Link DIR-2640-US router firmware 1.01B04 contains an incorrect access control vulnerability where configuring PPPoE starts the quagga routing daemon exposed via telnet using original default credentials and port. This allows unauthenticated attackers to gain full routing control, monitor all network traffic, hijack DNS, and perform phishing 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 data= 1.01b04CVSS 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
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/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.
-
Identify device model and firmware versionAccess the router's web interface under Status or Management section, or run 'cat /proc/version' or 'uname -a' via SSH/Telnet if available, to confirm the model is DIR-2640-US and firmware version is 1.01B04Affected if The device is a D-Link DIR-2640-US running firmware version 1.01B04
-
Verify PPPoE configuration statusLog into the router's web interface and navigate to Internet or WAN settings to check if PPPoE is enabled and configuredAffected if PPPoE is currently enabled or configured on the router
-
Check for exposed quagga telnet serviceUse a network port scanner (such as 'nmap' or 'netcat') to scan the router's external IP on port 23 (telnet) or attempt a telnet connection to the router's IP on port 23 to see if the quagga routing daemon is accessibleAffected if Telnet port 23 is open and responds, or a quagga routing prompt is accessible via telnet
-
Verify quagga service credentialsIf telnet access to quagga is possible, attempt login with the original default credentials (typically quagga/quagga or admin/admin) to confirm they have not been changedAffected if The quagga routing daemon is accessible via telnet using default credentials
The router is affected if it is a D-Link DIR-2640-US on firmware 1.01B04 with PPPoE enabled, and the quagga telnet service is exposed with default credentials still in use.
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 dataRemediate by changing default quagga credentials, disabling or firewall-filtering the telnet access to the routing daemon, and applying any available firmware updates. If PPPoE is not required, disable the feature entirely.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34203 — 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-2021-34203 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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