An authentication bypass vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.20 through 4.70, USG FLEX series firmware versions 4.50 through 5.20, ATP series firmware versions 4.32 through 5.20, VPN series firmware versions 4.30 through 5.20, and NSG series firmware versions V1.20 through V1.33 Patch 4, which could allow an attacker to bypass the web authentication and obtain administrative access of the device.

Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.

Firmware version 4.60 of Zyxel USG devices contains an undocumented account (zyfwp) with an unchangeable password. The password for this account can be found in cleartext in the firmware. This account can be used by someone to login to the ssh server or web interface with admin privileges.

The sensitive information exposure vulnerability in the CGI “Export_Log” and the binary “zcmd” in Zyxel DX5401-B0 firmware versions prior to V5.17(ABYO.1)C0 could allow a remote unauthenticated attacker to read the system files and to retrieve the password of the supervisor from the encrypted file.

A OS command injection vulnerability in the CGI program of Zyxel USG FLEX 100(W) firmware versions 5.00 through 5.21 Patch 1, USG FLEX 200 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 500 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 700 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 50(W) firmware versions 5.10 through 5.21 Patch 1, USG20(W)-VPN firmware versions 5.10 through 5.21 Patch 1, ATP series firmware versions 5.10 through 5.21 Patch 1, VPN series firmware versions 4.60 through 5.21 Patch 1, which could allow an attacker to modify specific files and then execute some OS commands on a vulnerable device.

The Open Connectivity Foundation UPnP specification before 2020-04-17 does not forbid the acceptance of a subscription request with a delivery URL on a different network segment than the fully qualified event-subscription URL, aka the CallStranger issue.

A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server does not run as the root user, ZyXEL devices include a setuid utility that can be leveraged to run any command with root privileges. As such, it should be assumed that exploitation of this vulnerability can lead to remote code execution with root privileges. By sending a specially-crafted HTTP POST or GET request to a vulnerable ZyXEL device, a remote, unauthenticated attacker may be able to execute ar…

**UNSUPPORTED WHEN ASSIGNED** Insecure default credentials for the Telnet function in the legacy DSL CPE Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 could allow an attacker to log in to the management interface if the administrators have the option to change the default credentials but fail to do so.

**UNSUPPORTED WHEN ASSIGNED** A post-authentication command injection vulnerability in the management commands of the legacy DSL CPE Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615 could allow an authenticated attacker to execute operating system (OS) commands on an affected device via Telnet.