IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2023-28771|Auth: none — unauthenticated|Reboot: required|Manual only

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

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.

Published Apr 25, 2023 · Updated May 17, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2023-06-21 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a OS Command Injection (CWE-78) vulnerability in Zyxel Multiple Firewalls. 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

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Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●IT Security
●Running atp100 firmware: 4.60 ≤ v < 5.36; atp100w firmware: 4.60 ≤ v < 5.35; atp200 firmware: 4.60 ≤ v < 5.36; atp500 firmware: 4.60 ≤ v < 5.36; atp700 firmware: 4.60 ≤ v < 5.36; atp800 firmware: 4.60 ≤ v < 5.36; usg flex 100 firmware: 4.60 ≤ v < 5.36; usg flex 100w firmware: 4.60 ≤ v < 5.36; usg flex 200 firmware: 4.60 ≤ v < 5.36; usg flex 50 firmware: 4.60 ≤ v < 5.36; usg flex 500 firmware: 4.60 ≤ v < 5.36; usg flex 50w firmware: 4.60 ≤ v < 5.36; usg flex 700 firmware: 4.60 ≤ v < 5.36; vpn100 firmware: 4.60 ≤ v < 5.36; vpn1000 firmware: 4.60 ≤ v < 5.36; vpn300 firmware: 4.60 ≤ v < 5.36; vpn50 firmware: 4.60 ≤ v < 5.36; zywall usg 310 firmware: 4.60 ≤ v < 4.73, 4.73; zywall usg 100 firmware: 4.60 ≤ v < 4.73, 4.73
Real-world incidentsWhat we've seen

Active exploitation documented in the wild. Threat-research write-up: http://packetstormsecurity.com/files/172820/Zyxel-IKE-Packet-Decoder-Unauthenticated-Remote-Code-Execution.html

How to patch

Manual remediation steps

1
Identify affected hosts: query inventory for general installs in scope.
2
Apply the vendor security update referenced in CVE-2023-28771's advisory. No specific KB/version is encoded yet — consult the linked MSRC/vendor URL.
3
Verify the fix per the vendor's published verification steps.
4
Document the remediation in your change ticket and re-scan with your vulnerability scanner to confirm closure.
PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2023-28771↗ MSRC Advisory↗ NVD↗ Vendor Advisory