CVE-2021-34991
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 · uneditedThis vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400v2 1.0.4.106_10.0.80 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the UPnP service, which listens on TCP port 5000 by default. When parsing the uuid request header, the process does not properly validate the length of user-supplied data prior to copying it to a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-14110.
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 confidenceStack-based buffer overflow in the UPnP service (TCP port 5000) of NETGEAR R6400v2 routers. The uuid request header is not properly validated for length before being copied to a fixed-size stack buffer, allowing unauthenticated network-adjacent attackers to achieve root-level code execution.
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< 1.0.0.94< 1.0.0.94< 1.0.0.66< 1.0.0.66< 1.0.1.76< 1.0.4.120< 1.0.4.120< 1.3.3.142CVSS 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
- High
CVSS:3.1/AV:A/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 checksWork through these to decide whether this CVE applies to you.
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Identify router modelLocate the model number on the router device label or log into the router admin interface (typically 192.168.1.1) and check the device information pageAffected if The model is one of: Ex3700, Ex3800, Ex6120, Ex6130, R6400, R6400v2, R6700v3, or R6900p
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Check installed firmware versionIn the router admin interface, navigate to the Firmware Update or Administration section and note the current firmware version displayedAffected if The firmware version is lower than the affected threshold for your model (Ex3700/Ex3800: < 1.0.0.94, Ex6120/Ex6130: < 1.0.0.66, R6400: < 1.0.1.76, R6400v2/R6700v3: < 1.0.4.120, R6900p: < 1.3.3.142)
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Verify UPnP service statusIn the router admin interface, go to the UPnP settings (usually under Advanced > Advanced Setup > UPnP) and check if UPnP is enabledAffected if UPnP is enabled and the device is a vulnerable model with an affected firmware version
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Check if TCP port 5000 is accessibleFrom a network-adjacent host, run a port scan targeting the router IP on TCP port 5000 (e.g., nmap -p 5000 <router_ip> or telnet <router_ip> 5000)Affected if TCP port 5000 is open and responding, combined with a vulnerable model/firmware combination
You are affected if your router model is one of the listed Ex or R series NETGEAR routers, your firmware version is below the specified threshold, UPnP is enabled, and TCP port 5000 is accessible on your network.
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.
dbcve · scoped1.0.0.661.0.0.941.0.1.76
Apply the vendor-supplied firmware update from NETGEAR. As an interim control, block TCP port 5000 at the network perimeter or disable UPnP if the router interface supports it.
Ex3700/Ex3800: 1.0.0.94 | Ex6120/Ex6130: 1.0.0.66 | R6400: 1.0.1.76 | R6400v2/R6700v3: 1.0.4.120 | R6900p: 1.3.3.142
- 1. Identify the exact NETGEAR router model from the affected list (Ex3700, Ex3800, Ex6120, Ex6130, R6400, R6400v2, R6700v3, or R6900p)
- 2. Download the firmware update from the official NETGEAR support website (kb.netgear.com) for your specific model
- 3. Navigate to the router's web administration interface (typically at 192.168.1.1)
- 4. Go to the Administration > Firmware Update section
- 5. Upload and apply the fixed firmware version for your model: Ex3700/Ex3800 to 1.0.0.94, Ex6120/Ex6130 to 1.0.0.66, R6400 to 1.0.1.76, R6400v2/R6700v3 to 1.0.4.120, or R6900p to 1.3.3.142
- 6. Wait for the router to reboot and confirm the firmware version has been updated successfully
- 7. Verify that the UPnP service on TCP port 5000 is now running the patched version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation16.0 h
- Testing12.0 h
- Review / QA8.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-34991 — 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-2021-34991 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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- Version or environment caveats, and links to real fixes
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