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Vulnerability Assessment

Weakness
CWE
CWE-120
ASVS 5.0
V15 - Secure Coding and Architecture Buffer copy size validation
MITRE ATT&CK

1 technique across 1 tactic: Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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Impact

CVSS score of 9.8 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required.
Exploit ScenarioDerived

A remote attacker could overflow a buffer to corrupt adjacent memory by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability.
Act Now Prioritize within 24-48h. Why: CRITICAL + in CISA KEV (actively exploited), no patch available.
Exploited in the wild (CISA KEV) No patch listed yet 28.8% exploitation probability (EPSS)

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AnalysisAI

A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Always validate buffer sizes before copy operations. Use bounded functions (strncpy, snprintf). Enable compiler protections.

Affects your stack

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Technical ContextAI · show details

This vulnerability is classified as Buffer Copy without Size Check (CWE-120), which allows attackers to overflow a buffer to corrupt adjacent memory. A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 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. Affected products include: Zyxel Atp100 Firmware, Zyxel Atp200 Firmware, Zyxel Atp500 Firmware, Zyxel Atp100W Firmware, Zyxel Atp700 Firmware. Version information: through 5.36.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Added to CISA KEV
Jul 14, 2026 - 04:22 CISA
CVE Published
May 24, 2023 - 13:15 nvd
CRITICAL 9.8

DescriptionNVD

A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 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.

Threat Intelligence Overview

EPSS Score
28.8%
Top 2% exploitable
Data Quality
2 sources
Confidence: Low
NVD CVE.org CISA KEV EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV Yes
Public POC No
EPSS 28.8%
Patch available No
Active threat Yes
Deciding rule
CRITICAL + in CISA KEV (actively exploited), no patch available
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Immediate
Exploitation· derived
Active
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact· derived
High

Priority Score

128
Low Medium High Critical
KEV: +50
EPSS: +29
CVSS: +49
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)NVD

cpe:2.3:o:zyxel:atp100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:5.36:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:5.36:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:5.36:-:*:*:*:*:*:*
+ 47 more

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CVE-2022-26531 HIGH
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Multiple improper input validation flaws were identified in some CLI commands of Zyxel USG/ZyWALL series firmware versio
CVE-2022-0910 MEDIUM
6.5 May 24

A downgrade from two-factor authentication to one-factor authentication vulnerability in the CGI program of Zyxel USG/Zy
CVE-2022-0734 MEDIUM
6.1 May 24

A cross-site scripting vulnerability was identified in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.35
CVE-2018-9129 MEDIUM
5.9 Aug 15

ZyXEL ZyWALL/USG series devices have a Bleichenbacher vulnerability in their Internet Key Exchange (IKE) handshake imple

Same weakness CWE-120 – Classic Buffer Overflow

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CVE-2017-7269 CRITICAL POC
9.8
CVE-2019-11043 CRITICAL POC
9.8
CVE-2016-10174 CRITICAL POC
9.8
CVE-2016-0099 HIGH POC
7.8
CVE-2016-6366 HIGH POC
8.8
CVE-2013-1331 HIGH
7.8
CVE-2013-0641 HIGH
7.8
CVE-2017-15222 CRITICAL POC
9.8

Same technique RCE

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CVE-2021-44228 CRITICAL POC
10.0
CVE-2022-47966 CRITICAL POC
9.8
CVE-2012-4681 CRITICAL POC
9.8
CVE-2023-3519 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2016-4117 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
9.8

References

Advisories & patches
ADVISORY https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls REF https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-33010

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