A directory traversal vulnerability caused by specific character sequences within an improperly sanitized URL was identified in some CGI programs of Zyxel USG FLEX 100(W) firmware versions 4.50 through 5.30, USG FLEX 200 firmware versions 4.50 through 5.30, USG FLEX 500 firmware versions 4.50 through 5.30, USG FLEX 700 firmware versions 4.50 through 5.30, USG FLEX 50(W) firmware versions 4.16 through 5.30, USG20(W)-VPN firmware versions 4.16 through 5.30, ATP series firmware versions 4.32 through 5.30, VPN series firmware versions 4.30 through 5.30, USG/ZyWALL series firmware versions 4.11 through 4.72, that could allow an authenticated attacker to access some restricted files on a vulnerable device.

A argument injection vulnerability in the 'packet-trace' CLI command of Zyxel USG/ZyWALL series firmware versions 4.09 through 4.71, USG FLEX series firmware versions 4.50 through 5.21, ATP series firmware versions 4.32 through 5.21, VPN series firmware versions 4.30 through 5.21, NSG series firmware versions 1.00 through 1.33 Patch 4, NXC2500 firmware version 6.10(AAIG.3) and earlier versions, NAP203 firmware version 6.25(ABFA.7) and earlier versions, NWA50AX firmware version 6.25(ABYW.5) and earlier versions, WAC500 firmware version 6.30(ABVS.2) and earlier versions, and WAX510D firmware version 6.30(ABTF.2) and earlier versions, that could allow a local authenticated attacker to execute arbitrary OS commands by including crafted arguments to the CLI command.

Multiple improper input validation flaws were identified in some CLI commands of Zyxel USG/ZyWALL series firmware versions 4.09 through 4.71, USG FLEX series firmware versions 4.50 through 5.21, ATP series firmware versions 4.32 through 5.21, VPN series firmware versions 4.30 through 5.21, NSG series firmware versions 1.00 through 1.33 Patch 4, NXC2500 firmware version 6.10(AAIG.3) and earlier versions, NAP203 firmware version 6.25(ABFA.7) and earlier versions, NWA50AX firmware version 6.25(ABYW.5) and earlier versions, WAC500 firmware version 6.30(ABVS.2) and earlier versions, and WAX510D firmware version 6.30(ABTF.2) and earlier versions, that could allow a local authenticated attacker to cause a buffer overflow or a system crash via a crafted payload.

A downgrade from two-factor authentication to one-factor authentication vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.32 through 4.71, USG FLEX series firmware versions 4.50 through 5.21, ATP series firmware versions 4.32 through 5.21, and VPN series firmware versions 4.32 through 5.21, that could allow an authenticated attacker to bypass the second authentication phase to connect the IPsec VPN server even though the two-factor authentication (2FA) was enabled.

A cross-site scripting vulnerability was identified in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.35 through 4.70, USG FLEX series firmware versions 4.50 through 5.20, ATP series firmware versions 4.35 through 5.20, and VPN series firmware versions 4.35 through 5.20, that could allow an attacker to obtain some information stored in the user's browser, such as cookies or session tokens, via a malicious script.

An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versions 4.35 through 4.64 and USG Flex, ATP, and VPN series firmware versions 4.35 through 5.01, which could allow a remote attacker to execute arbitrary commands on an affected device.

Certain Zyxel products allow command injection by an admin via an input string to chg_exp_pwd during a password-change action. This affects VPN On-premise before ZLD V4.39 week38, VPN Orchestrator before SD-OS V10.03 week32, USG before ZLD V4.39 week38, USG FLEX before ZLD V4.55 week38, ATP before ZLD V4.55 week38, and NSG before 1.33 patch 4.

ZyXEL ZyWALL USG 2.12 AQQ.2 and 3.30 AQQ.7 devices are affected by a CSRF vulnerability via a cgi-bin/zysh-cgi cmd action to add a user account. This account's access could, for example, subsequently be used for stored XSS.

ZyXEL ZyWALL/USG series devices have a Bleichenbacher vulnerability in their Internet Key Exchange (IKE) handshake implementation used for IPsec based VPN connections.