CVE-2023-34139

Unauthenticated OS command execution via Free Time WiFi

Published Jul 17, 2023 · Updated Oct 29, 2024

Command injection in Zyxel USG FLEX 4.50 through 5.36 Patch 2 and VPN 4.20 through 5.36 Patch 2 allows remote attackers to run OS commands. The flaw is in the Free Time WiFi hotspot feature, but Zyxel has not disclosed the request field or command-construction operation that mishandles input. An unauthenticated attacker must be on the LAN; successful exploitation runs commands on the firewall and can alter device data or operation.

CVSS severity8.8
High
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Command injection in Zyxel USG FLEX 4.50 through 5.36 Patch 2 and VPN 4.20 through 5.36 Patch 2 allows remote attackers to run OS commands. The flaw is in the Free Time WiFi hotspot feature, but Zyxel has not disclosed the request field or command-construction operation that mishandles input. An unauthenticated attacker must be on the LAN; successful exploitation runs commands on the firewall and can alter device data or operation.

The record

CVE
CVE-2023-34139
Published
Jul 17, 2023
Updated
Oct 29, 2024
Vendor
Zyxel Networks
Product
USG FLEX Series Firmware
Classifications
CWE-78, T1059
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 29, 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=4.50 <=5.36_Patch-2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zyxel Networks · USG FLEX Series Firmwareversion=4.50 <=5.36_Patch-2
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.20 through 5.36 Patch 2
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.50 through 5.36 Patch 2
Zyxel Networks · Zyxel VPN Firewall Firmwareversion=4.20 <=5.36_Patch-2

Published CVSS scores

8.8Zyxel CorporationCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1059Command and Scripting Interpreter

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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