CVE-2023-4398Network attack vector

Device crash via QuickSec IKE integer overflow

Published Nov 28, 2023 · Updated Oct 17, 2024

Integer overflow in QuickSec IPsec in Zyxel firewall firmware through 5.37 allows remote attackers to crash devices via crafted IKE packets. The vendor identifies the QuickSec IPsec toolkit in the VPN feature, but does not disclose which IKE field or arithmetic operation overflows. The IKE service must be reachable; no authentication or user interaction is required, and successful exploitation interrupts firewall availability.

CVSS severity7.5
High
EPSS probability0.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in QuickSec IPsec in Zyxel firewall firmware through 5.37 allows remote attackers to crash devices via crafted IKE packets. The vendor identifies the QuickSec IPsec toolkit in the VPN feature, but does not disclose which IKE field or arithmetic operation overflows. The IKE service must be reachable; no authentication or user interaction is required, and successful exploitation interrupts firewall availability.

The record

CVE
CVE-2023-4398
Published
Nov 28, 2023
Updated
Oct 17, 2024
Vendor
Zyxel Networks
Product
Zyxel USG FLEX 50W Firmware
Classifications
CWE-190, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 28, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 17, 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=4.16 <=5.37

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Zyxel USG FLEX 50W Firmwareversion=4.16 <=5.37
Zyxel Networks · Zyxel USG FLEX 50(W) Series Firmwareversion=versions 4.16 through 5.37
Zyxel Networks · USG20W-VPN Firmwareversion=4.16 <=5.37
Zyxel Networks · Zyxel ATP Series Firmwareversion=4.32 <=5.37; version=versions 4.32 through 5.37
Zyxel Networks · Zyxel USG20(W)-VPN Series Firmwareversion=versions 4.16 through 5.37
Zyxel Networks · Zyxel VPN Series Firmwareversion=5.30 <=5.37; version=versions 4.30 through 5.37
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.50 <=5.37; version=versions 4.50 through 5.37

Published CVSS scores

7.5Zyxel CorporationCVSS:3.1/AV:N/AC:L/PR:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
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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