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Findings

CVE-2023-33009

Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Published May 24, 2023 · updated Jun 16, 2026 · zyxel atp100 firmware

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.

Timeline

Detection, updates, and resolution for this record.

  1. May 24, 2023 · Catalog

    Detected

    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 4.6

  2. Jun 5, 2023 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Jun 26, 2023 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Jun 16, 2026 · Catalog

    Updated

    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 4.6

Required action

Apply updates per vendor instructions.

CISA due date Jun 26, 2023

Affected

  • cpe zyxel/atp100 firmwareversion unspecified
  • cpe zyxel/atp100 firmware5.36
  • cpe zyxel/atp100w firmwareversion unspecified
  • cpe zyxel/atp200 firmwareversion unspecified
  • cpe zyxel/atp200 firmware5.36
  • cpe zyxel/atp500 firmwareversion unspecified
  • cpe zyxel/atp500 firmware5.36
  • cpe zyxel/atp700 firmwareversion unspecified
  • cpe zyxel/atp800 firmwareversion unspecified
  • cpe zyxel/usg flex 100 firmwareversion unspecified
  • vendor Zyxel Multiple Firewallsversion unspecified

Sources

  • CISA KEVCVE-2023-33009

    Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls contain a buffer overflow vulnerability in the notification function that could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and remote code execution on an affected device.

    cisa.gov
  • CVE.orgCVE-2023-33009

    Official CVE identifier

    cve.org
  • FIRST EPSSCVE-2023-33009

    30-day exploitation probability 28.1%

    first.org
  • NIST NVDCVE-2023-33009

    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.

    nvd.nist.gov

References