CVE-2023-33009: Zyxel Multiple Firewalls Buffer Overflow, actively exploited

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Zyxel Atp100 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Atp100w Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Atp200 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Atp500 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Atp700 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Atp800 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg20-vpn Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg 20w-vpn Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg 40 Firmware≥ 4.60 < 4.73 · 4.73

Zyxel Usg 40w Firmware≥ 4.60 < 4.73 · 4.73

Zyxel Usg 60 Firmware≥ 4.60 < 4.73 · 4.73

Zyxel Usg 60w Firmware≥ 4.60 < 4.73 · 4.73

Zyxel Usg Flex 100 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 100w Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 200 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 500 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 50 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 50w Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Usg Flex 700 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Vpn1000 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Vpn100 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Vpn300 Firmware≥ 4.60 < 5.36 · 5.36

Zyxel Vpn50 Firmware≥ 4.60 < 5.36 · 5.36

Remediation

Fixed in

Zyxel Atp100 Firmware≥ 5.36

Zyxel Atp100w Firmware≥ 5.36

Zyxel Atp200 Firmware≥ 5.36

Zyxel Atp500 Firmware≥ 5.36

Zyxel Atp700 Firmware≥ 5.36

Zyxel Atp800 Firmware≥ 5.36

Zyxel Usg20-vpn Firmware≥ 5.36

Zyxel Usg 20w-vpn Firmware≥ 5.36

Zyxel Usg 40 Firmware≥ 4.73

Zyxel Usg 40w Firmware≥ 4.73

Patch & vendor advisories

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2023-33009 being actively exploited?

Yes. CVE-2023-33009 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 5 Jun 2023.

How severe is CVE-2023-33009?

CVE-2023-33009 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 28.1% probability of exploitation.

Which products are affected by CVE-2023-33009?

Affected products include Zyxel Atp100 Firmware, Zyxel Atp100w Firmware, Zyxel Atp200 Firmware, Zyxel Atp500 Firmware, Zyxel Atp700 Firmware, and 18 more.

How do I fix CVE-2023-33009?

Upgrade affected software to a fixed version, for example Zyxel Atp100 Firmware 5.36, Zyxel Atp100w Firmware 5.36, Zyxel Atp200 Firmware 5.36 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2023-33009 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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