CVE-2023-33009 Zyxel Multiple Firewalls Buffer Overflow

Exploited in the wild Critical 9.8 Published 24 May 2023 Updated 21 Oct 2025

Unauthenticated attackers can trigger a buffer overflow in Zyxel firewall firmware, leading to remote code execution or denial of service.

Exploited in the wild: Since 5 Jun 2023
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2023-33009?

CVE-2023-33009 is a critical memory corruption vulnerability in Zyxel ATP series firmware, published on 24 May 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX series firmware versions 4.60 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.60 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.60 through 5.36 Patch 1, VPN series firmware versions 4.60 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.60 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

Weakness: CWE-120

Which versions are affected by CVE-2023-33009?

It affects 23 products.

Products include Zyxel Atp100 Firmware, Zyxel Atp100w Firmware, Zyxel Atp200 Firmware, Zyxel Atp500 Firmware, Zyxel Atp700 Firmware, Zyxel Atp800 Firmware and 17 more.

How do I fix CVE-2023-33009?

No fix has been published for CVE-2023-33009 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 26 Jun 2023.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2023-33009 being exploited?

Yes. Attackers have exploited CVE-2023-33009 in the wild since at least 5 Jun 2023.

Sources

Also known as GHSA-g3f9-6h7x-x69v.