# CVE-2023-33009: Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Source: https://junglewise.ai/threats/cve-2023-33009-zyxel-multiple-firewalls-buffer-overflow-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2023-06-05. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-2023-33009 · Severity: critical · CVSS 9.8 · Exploited in the wild · Published 2023-06-05

A buffer overflow vulnerability exists in the notification function of multiple Zyxel firewall series. An unauthenticated remote attacker can exploit this to cause a denial-of-service (DoS) condition or execute arbitrary code on the affected device.

Technologies: [Zyxel Firewalls](https://junglewise.ai/threats/technologies/firewalls), [Zyxel Multiple Firewalls](https://junglewise.ai/threats/technologies/multiple-firewalls). Vendors: [Zyxel](https://junglewise.ai/threats/vendors/zyxel).

## Quick answers

**Is CVE-2023-33009 exploited in the wild?** Yes. CVE-2023-33009 is known to be exploited in the wild, first recorded on 5 June 2023. Treat it as urgent.

**How severe is CVE-2023-33009?** Critical severity, with a CVSS score of 9.8, published 5 June 2023.

**Which products and versions are affected?** Zyxel ATP series firmware 4.60 through 5.36 Patch 1; Zyxel USG FLEX series firmware 4.60 through 5.36 Patch 1; Zyxel USG FLEX 50(W) firmware 4.60 through 5.36 Patch 1; Zyxel USG20(W)-VPN firmware 4.60 through 5.36 Patch 1; and 2 more.

**Is there a fix for CVE-2023-33009?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2023-33009 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2023-33009?** Check whether you run Zyxel Firewalls or Zyxel Multiple Firewalls. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- Zyxel ATP series firmware 4.60 through 5.36 Patch 1
- Zyxel USG FLEX series firmware 4.60 through 5.36 Patch 1
- Zyxel USG FLEX 50(W) firmware 4.60 through 5.36 Patch 1
- Zyxel USG20(W)-VPN firmware 4.60 through 5.36 Patch 1
- Zyxel VPN series firmware 4.60 through 5.36 Patch 1
- Zyxel ZyWALL/USG series firmware 4.60 through 4.73 Patch 1

## Timeline

- 2023-05-24: disclosed: Date based on CVE ID assignment/early reporting context
- 2023-06-05: advisory
- 2023-06-05: kev added: Added to CISA Known Exploited Vulnerabilities Catalog
- 2023-06-05: exploited: Confirmed as exploited in the wild per CISA KEV catalog and advisory.

## Related threats

- [Zyxel Multiple Firewalls Path Traversal Vulnerability](https://junglewise.ai/threats/cve-2024-11667-zyxel-multiple-firewalls-path-traversal-vulnerability)
- [Zyxel Multiple Firewalls Buffer Overflow Vulnerability](https://junglewise.ai/threats/cve-2023-33010-zyxel-multiple-firewalls-buffer-overflow-vulnerability)
- [Zyxel Multiple Firewalls OS Command Injection Vulnerability](https://junglewise.ai/threats/cve-2023-28771-zyxel-multiple-firewalls-os-command-injection-vulnerability)
- [Zyxel Multiple Firewalls OS Command Injection Vulnerability](https://junglewise.ai/threats/cve-2022-30525-zyxel-multiple-firewalls-os-command-injection-vulnerability)