CVE-2023-4397

Administrator-triggered denial of service via crafted CLI strings

Published Nov 28, 2023 · Updated Aug 2, 2024

Buffer overflow in Zyxel firewall firmware 5.37 allows local users with administrator privileges to interrupt device service. The affected CLI command mishandles crafted strings and overflows a buffer; Zyxel has not disclosed the command or faulty copy operation. Exploitation requires authenticated administrator CLI access and affects availability only, with no reported data disclosure or modification.

CVSS severity4.4
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Zyxel firewall firmware 5.37 allows local users with administrator privileges to interrupt device service. The affected CLI command mishandles crafted strings and overflows a buffer; Zyxel has not disclosed the command or faulty copy operation. Exploitation requires authenticated administrator CLI access and affects availability only, with no reported data disclosure or modification.

The record

CVE
CVE-2023-4397
Published
Nov 28, 2023
Updated
Aug 2, 2024
Vendor
Zyxel Networks
Product
USG20(W)-VPN Series
Classifications
CWE-120, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Nov 28, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.37

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Zyxel Networks · USG20(W)-VPN Seriesversion=5.37
Zyxel Networks · USG FLEX 50 Seriesversion=5.37
Zyxel Networks · ATP Seriesversion=5.37
Zyxel Networks · USG FLEX Seriesversion=5.37

Published CVSS scores

4.4Zyxel CorporationCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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