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Fencer Vulns
high 8.8

CVE-2023-34139 json

A command injection vulnerability in the Free Time WiFi hotspot feature of the Zyxel USG FLEX series firmware versions 4.50 through 5.36 Pa…

published 2023-07-17 3 y ago modified 2026-06-17 4 mo ago also EUVD-2023-38241

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

A command injection vulnerability in the Free Time WiFi hotspot feature of the Zyxel USG FLEX series firmware versions 4.50 through 5.36 Patch 2 and VPN series firmware versions 4.20 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands on an affected device.

Patch / fix

  • zyxel usg_2200-vpn_firmware 5.37
  • zyxel usg_flex_100_firmware 5.37
  • zyxel usg_flex_100w_firmware 5.37
  • zyxel usg_flex_200_firmware 5.37
  • zyxel usg_flex_50_firmware 5.37
  • zyxel usg_flex_500_firmware 5.37
  • zyxel usg_flex_50w_firmware 5.37
  • zyxel usg_flex_700_firmware 5.37
  • zyxel zywall_vpn100_firmware 5.37
  • zyxel zywall_vpn2s_firmware 5.37
  • zyxel zywall_vpn300_firmware 5.37
  • zyxel zywall_vpn50_firmware 5.37
  • zyxel zywall_vpn_100_firmware 5.37
  • zyxel zywall_vpn_300_firmware 5.37
  • zyxel zywall_vpn_50_firmware 5.37

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2 y ago

Exploit prediction

0.76% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 8.8 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Zyxel USG FLEX series firmware
  • Zyxel VPN series firmware
  • zyxel usg_flex_firmware
  • zyxel vpn_firmware

Classification

Weakness
  • CWE-78 Improper Neutralization of Special Elements used in an OS Command

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.