CVE-2021-31755 — AI Deep Analysis Summary

🚨 **Essence**: A stack buffer overflow in Tenda AC11 routers. 📉 **Consequences**: Attackers can execute arbitrary code on the device via a crafted POST request to `/goform/setmac`. Total device compromise is possible.

🛠️ **Root Cause**: Stack Buffer Overflow. 💥 **Flaw**: The `/goform/setmac` endpoint fails to properly validate input length, allowing malicious data to overflow the buffer and hijack execution flow.

📱 **Device**: Tenda AC11 Router. 📦 **Affected Versions**: Firmware version **02.03.01.104_CN** and all earlier versions. ⚠️ If you have this router, you are at risk.

💻 **Privileges**: Arbitrary Code Execution (RCE). 🕵️ **Impact**: Hackers gain full control over the router. They can run commands, steal network data, or use the device as a botnet node. No user interaction needed.

🔓 **Auth Status**: Unauthenticated. 🌐 **Threshold**: LOW. Attackers do NOT need to log in. A simple remote POST request is enough to trigger the vulnerability. Extremely easy to exploit.

🔥 **Exploit Availability**: YES. Public POCs exist on GitHub (e.g., `r3s3tt/CVE-2021-31755`). 🧪 Tools like Nuclei also have templates. Wild exploitation is highly likely given the ease of access.

🔍 **Self-Check**: Scan for Tenda AC11 devices. 📡 Check if firmware is <= 02.03.01.104_CN. 🛠️ Use Nuclei templates or custom scripts targeting the `/goform/setmac` endpoint to verify susceptibility.

🛡️ **Fix**: Update firmware to the latest version provided by Tenda. 📥 **Action**: Check Tenda's official support page for AC11. Install the patch immediately to close the buffer overflow gap.

🚧 **No Patch?**: Block external access to the router's web management interface. 🚫 **Mitigation**: Disable remote management features. If possible, isolate the router in a segmented network to limit lateral movement.

🔴 **Priority**: CRITICAL. ⚡ **Urgency**: HIGH. Since it is unauthenticated and allows RCE, this is a top-priority vulnerability. Patch immediately or face potential compromise.