CVE-2021-31755 Tenda AC11 Router Stack Buffer Overflow Vulnerability
Tenda AC11 devices contain a stack buffer overflow vulnerability in /goform/setmac which allows attackers to execute code via a crafted post request.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
- Rated Critical severity (CVSS 9.8, scored by CISA).
- This product type is often exposed to the internet, which is where attackers scan for it first.
- It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
An 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.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Tenda AC11 Router. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
- 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
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