Zyxel Security Advisory for WiFi Simple Config Buffer Overflow Vulnerabilities

CVE: CVE-2021-35392, CVE-2021-35393



Zyxel is aware of two buffer overflow vulnerabilities in the WiFi Simple Config of Realtek’s Software Development Kit (SDK) for WiFi products and will release patch for the vulnerable product on the market. Users are advised to install the applicable firmware update for optimal protection.


What is the vulnerability?

The first vulnerability is a stack buffer overflow that is present due to unsafe parsing of the UPnP SUBSCRIBE/UNSUBSCRIBE Callback header. The second vulnerability is a heap buffer overflow that is present due to unsafe crafting of SSDP NOTIFY messages from received M-SEARCH messages.


What versions are vulnerable—and what should you do?

After a thorough investigation, we’ve identified one vulnerable product that is within its warranty and support period and will release firmware patch to address the issues, as shown in the table below.

Affected model Patch availability
WAP6804 V1.00 (ABKH.9)C0 in Q4 2021*

*Please reach out to your local Zyxel support team for the file.


Please note that the P-330W, X150N, NBG-2105, NBG-416N, and NBG-418N models mentioned in a report by IoT Inspector entered end-of-life years previously; therefore, firmware updates are no longer provided for them. We recommend that users with these models replace them with newer-generations products, which typically come with improved designs that better suit current applications.


Got a question?

Please contact your local service rep or visit Zyxel’s forum for further information or assistance.



Thanks to IoT Inspector GmbH for reporting the issues to us.


Revision history

2021-8-16: Initial release