CVE-2023-34140

Service interruption via crafted CAPWAP request

Published Jul 17, 2023 · Updated Oct 21, 2024

Buffer overflow in the CAPWAP daemon in affected Zyxel firewall and WLAN controller firmware allows remote attackers on the LAN to interrupt service. Zyxel has not disclosed the affected function or the exact unchecked buffer operation within the daemon. No authentication is required, but the attacker must reach the device over the LAN; successful exploitation causes only denial of service.

CVSS severity6.5
Medium
EPSS probability0.30%
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 the CAPWAP daemon in affected Zyxel firewall and WLAN controller firmware allows remote attackers on the LAN to interrupt service. Zyxel has not disclosed the affected function or the exact unchecked buffer operation within the daemon. No authentication is required, but the attacker must reach the device over the LAN; successful exploitation causes only denial of service.

The record

CVE
CVE-2023-34140
Published
Jul 17, 2023
Updated
Oct 21, 2024
Vendor
Zyxel Networks
Product
Zyxel USG FLEX 50(W) Series Firmware
Classifications
CWE-120, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 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 through 5.36 Patch 2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Zyxel USG FLEX 50(W) Series Firmwareversion=4.16 through 5.36 Patch 2
Zyxel Networks · Zyxel NXC2500 Firmwareversion=6.10(AAIG.0) through 6.10(AAIG.3)
Zyxel Networks · Zyxel ATP Series Firmwareversion=4.32 through 5.36 Patch 2
Zyxel Networks · Zyxel USG20(W)-VPN Series Firmwareversion=4.16 through 5.36 Patch 2
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.30 through 5.36 Patch 2
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.50 through 5.36 Patch 2
Zyxel Networks · Zyxel NXC5500 Firmwareversion=6.10(AAOS.0) through 6.10(AAOS.4)

Published CVSS scores

6.5Zyxel CorporationCVSS:3.1/AV:A/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)
Vectoradjacent
Privilegesunauthenticated
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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