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Weekly Signal
Live intelligence Updated 20 Aug 2026 · 23:28 UTC

Zyxel · Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +21 more

CVE-2023-33009

Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Recommended action

Validate affected assets and exposure now, then remediate on an accelerated schedule. Vendor advisory from www.zyxel.com

View response plan
CVSS9.8
EPSS28.1%
KEVYes
ExploitationConfirmed exploitation
RemediationNot yet verified ↓

Assessment

Why it matters

CISA lists this vulnerability as known to be exploited; exploitation is confirmed; EPSS is 28.1%; technical severity is CVSS 9.8.

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.

Who should care

  • Teams operating Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +21 more
  • Vulnerability and exposure management teams
  • Security operations teams monitoring exploitation activity

Response plan

What I would do

  1. Confirm whether Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +21 more is present in the environment.
  2. Identify affected versions and establish whether vulnerable services are exposed or reachable.
  3. Vendor advisory from www.zyxel.com
  4. Review relevant security telemetry for evidence of attempted or successful exploitation.
  5. Document the remediation decision and track it to verified completion.

Treatment intelligence

Remediation intelligence

Not yet verified

Vendor sources are listed before government and third-party guidance. Confirm product applicability and change prerequisites before deployment.

Verification noteAutomated link verification has not completed for this guidance yet.

Required Action

Technical details

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-120
Affected versions
Zyxel Atp100 Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Atp100w Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Atp200 Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Atp500 Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Atp700 Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Atp800 Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36); Zyxel Multiple Firewalls; Zyxel Usg 20w-vpn Firmware (Start Including 4.60, End Excluding 5.36 | Version 5.36 | Version 5.36)
Fixed versions
Zyxel Atp100 Firmware (Fixed from 5.36); Zyxel Atp100w Firmware (Fixed from 5.36); Zyxel Atp200 Firmware (Fixed from 5.36); Zyxel Atp500 Firmware (Fixed from 5.36); Zyxel Atp700 Firmware (Fixed from 5.36); Zyxel Atp800 Firmware (Fixed from 5.36); Zyxel Usg 20w-vpn Firmware (Fixed from 5.36); Zyxel Usg 40 Firmware (Fixed from 4.73)
Published
24 May 2023
Attack vector
Network
Privileges required
None
User interaction
None

Signal timeline

  1. CVE published
  2. Added to CISA KEV
  3. Latest EPSS score: 28.1%
  4. Signal calculated at 75

External references

Live public intelligence This assessment combines public-source evidence. Validate the affected product, version and exposure against your own environment before making a risk decision.