---
id: "CVE-2021-31755"
kind: "vulnerability"
aliases: ["CVE-2021-31755"]
title: "Tenda AC11 Router: Tenda AC11 Router Stack Buffer Overflow Vulnerability"
severity: "critical"
cvss: 10.0
epss: 0.86511
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Tenda AC11 Router", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["ac11", "exploited", "infrastructure", "routers", "self-hosted", "tenda"]
not_affected_if: ["default-config"]
published_at: "2021-05-07T23:15:07+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T20:29:24+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-31755", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-31755", "first_seen_at": "2026-10-23T19:13:43+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-31755", "first_seen_at": "2026-10-23T19:35:23+00:00"}]
---

# Tenda AC11 Router: Tenda AC11 Router Stack Buffer Overflow Vulnerability

Tenda AC11 router firmware through 02.03.01.104_CN has a stack buffer overflow in the /goform/setmac handler. A remote attacker can send a crafted POST request to run arbitrary code on the device.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Tenda AC11 Router affected ? fixed ?

## How to check

Check the router's firmware version in its admin UI (System Status or similar) and compare it to 02.03.01.104_CN or earlier.

## Fix

Update to a firmware release newer than 02.03.01.104_CN from Tenda, or replace the device if no fixed firmware is available.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-31755
- 2026-10-23T19:13:43+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-31755
- 2026-10-23T19:35:23+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-31755

## From the sources

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.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_