CVE-2023-27992: Zyxel Multiple NAS Devices Command Injection Vulnerability

Critical severity, CVSS 9.8. Actively exploited: in CISA KEV since 2023-06-23. EPSS: 82.8% chance of exploitation in the next 30 days.

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.

Affected products

• Zyxel NAS326 Firmware: before 5.21\(aazf.14\)c0 (fixed in 5.21\(aazf.14\)c0)
• Zyxel NAS540 Firmware: before 5.21\(aatb.11\)c0 (fixed in 5.21\(aatb.11\)c0)
• Zyxel NAS542 Firmware: before 5.21\(abag.11\)c0 (fixed in 5.21\(abag.11\)c0)

Published 2023-06-19. Last modified 2026-06-17.