CVE-2021-31755
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 · uneditedAn issue was discovered on Tenda AC11 devices with firmware through 02.03.01.104_CN. A stack buffer overflow vulnerability in /goform/setmac allows attackers to execute arbitrary code on the system via a crafted post request.
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 confidenceA stack buffer overflow vulnerability exists in the Tenda AC11 router firmware (versions through 02.03.01.104_CN) in the /goform/setmac web endpoint. Attackers can send a specially crafted POST request with oversized input that overwrites stack memory, allowing arbitrary code execution with root privileges on the device.
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<= 02.03.01.104_cnCVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify the router modelAccess the router's web administration interface and check the device information page, or use Nmap to detect the device via HTTP response headers or favicon. Look for 'Tenda' or 'AC11' in the management page or SNMP/sysinfo responses.Affected if The device is a Tenda AC11 router.
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Check the firmware versionNavigate to the router's web interface (typically at 192.168.0.1) and locate the firmware version under System Settings, Firmware Upgrade, or Device Info. Alternatively, inspect the HTTP response from the router's login page for version strings, or use 'grep' on firmware binaries if you have extracted them.Affected if The firmware version is 02.03.01.104_cn or earlier.
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Confirm the web management interface is accessibleSend an HTTP GET request to the router's IP address (e.g., curl http://192.168.0.1) and verify a Tenda login page or API response is returned. Check if the /goform/setmac endpoint responds to requests.Affected if The router's web interface returns a valid HTTP response with Tenda-related content.
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Determine if the device is exposed to untrusted networksReview firewall rules, NAT configurations, or port forwarding settings to determine if TCP port 80/443 on the router is reachable from external networks. Use external port scanning tools (e.g., Nmap from outside your LAN) or check router firewall settings.Affected if The router's HTTP/HTTPS management ports are reachable from networks outside the local trusted LAN.
A user is affected if they are running Tenda AC11 firmware version 02.03.01.104_cn or earlier AND the router's web management interface (specifically the /goform/setmac endpoint) is accessible from an untrusted 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.
From vendor dataUpdate Tenda AC11 firmware to a version beyond 02.03.01.104_CN; if unavailable, restrict administrative interface to trusted networks or consider replacing the device with a actively supported model.
- Consultation4.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-31755 — 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-2021-31755 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
- No weaponised exploit code, or anything meant to cause harm
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