Zyxel security advisory for directory traversal and command injection vulnerabilities of VPN2S Firewall

CVE: CVE-2021-35027, CVE-2021-35028



Zyxel has released a patch addressing directory traversal and command injection vulnerabilities in the VPN2S firewall. Users are advised to install it for optimal protection.


What is the vulnerability?

A directory traversal vulnerability caused by specific character sequences within an improperly sanitized URL was identified in the VPN2S firewall. A command injection vulnerability caused by improper filtering for the parameters in a CGI program was also identified.


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 released a hotfix to address the issue, as shown in the table below.

Affected model Hotfix availability
ZyWALL VPN2S V1.20(ABLN.2)_00210624C1

Got a question?

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



Thanks to Qihoo 360 for reporting the issues to us.


Revision history

2021-9-30: Initial release