ClosedCriticalPatched

Zyxel Multiple Firewalls: OS Command Injection (CVE-2023-28771)

Zyxel Multiple Firewalls

Zyxel ATP, USG FLEX, VPN, and ZyWALL/USG firewalls allow for improper error message handling which could allow an unauthenticated attacker to execute OS commands remotely by sending crafted packets to an affected device. Added to CISA KEV on 2023-05-31.

Why this severity: CVSS 9.8 (NVD), actively exploited (CISA KEV)

Started: May 31, 2023
Closed: May 31, 2023
CVE: CVE-2023-28771

Follow this incident

Updated May 31, 2023

Affected

See vendor advisory / CISA notes (versions not always listed in KEV feed)

Fixed in

See vendor advisory linked in sources

Timeline1

May 31, 2023
CISA added CVE-2023-28771 to the KEV catalog (due 2023-06-21).

Advisories3

Notes & caveats

Derived from CISA KEV JSON feed catalogVersion 2026.10.21. Exact affected/fixed version strings are not always in the KEV record — verify against the vendor advisory URL. startedAt uses dateAdded (exploitation may have begun earlier).

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