What’s Vulnerable › Vulnerabilities

CVE-2023-27990

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-04-24 · updated 2026-06-17
• Weakness: CWE-79

Description

The cross-site scripting (XSS) vulnerability in Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow an authenticated attacker with administrator privileges to store malicious scripts in a vulnerable device. A successful XSS attack could then result in the stored malicious scripts being executed when the user visits the Logs page of the GUI on the device.

Affected products

• Zyxel Atp100 Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Atp100W Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Atp200 Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Atp500 Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Atp700 Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Atp800 Firmware: from 4.32 before 5.36 — fixed in 5.36
• Zyxel Usg20-Vpn Firmware: from 4.30 before 5.36 — fixed in 5.36
• Zyxel USG 20(W)-VPN firmware: from 4.16 before 5.36 — fixed in 5.36
• Zyxel firewall (ZLD): from 4.50 before 5.36 — fixed in 5.36
• Zyxel USG FLEX 100(W) firmware: from 4.50 before 5.36 — fixed in 5.36
• Zyxel USG FLEX 200 firmware: from 4.50 before 5.36 — fixed in 5.36
• Zyxel USG FLEX 500 firmware: from 4.50 before 5.36 — fixed in 5.36
• Zyxel Usg Flex 50 Firmware: from 4.50 before 5.36 — fixed in 5.36
• Zyxel USG FLEX 50(W) firmware: from 4.16 before 5.36 — fixed in 5.36
• Zyxel USG FLEX 700 firmware: from 4.50 before 5.36 — fixed in 5.36
• Zyxel Vpn1000 Firmware: from 4.30 before 5.36 — fixed in 5.36
• Zyxel Vpn100 Firmware: from 4.30 before 5.36 — fixed in 5.36
• Zyxel Vpn300 Firmware: from 4.30 before 5.36 — fixed in 5.36
• Zyxel Vpn50 Firmware: from 4.30 before 5.36 — fixed in 5.36

How to fix

Upgrade to a fixed version: Zyxel Atp100 Firmware 5.36; Zyxel Atp100W Firmware 5.36; Zyxel Atp200 Firmware 5.36; Zyxel Atp500 Firmware 5.36; Zyxel Atp700 Firmware 5.36; Zyxel Atp800 Firmware 5.36; Zyxel Usg20-Vpn Firmware 5.36; Zyxel USG 20(W)-VPN firmware 5.36; Zyxel firewall (ZLD) 5.36; Zyxel USG FLEX 100(W) firmware 5.36; Zyxel USG FLEX 200 firmware 5.36; Zyxel USG FLEX 500 firmware 5.36. Check the vendor advisory for mitigations.

References

• https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-xss-vulnerability-and-post-authentication-command-injection-vulnerability-in-firewalls
• https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-xss-vulnerability-and-post-authentication-command-injection-vulnerability-in-firewalls

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