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Fencer Vulns
medium 5.2

CVE-2023-35139 json

A cross-site scripting (XSS) vulnerability in the CGI program of the Zyxel ATP series firmware versions 5.10 through 5.37, USG FLEX series…

published 2023-11-28 2 y ago modified 2026-06-17 4 mo ago also EUVD-2023-39169

cvss
5.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

A cross-site scripting (XSS) vulnerability in the CGI program of the Zyxel ATP series firmware versions 5.10 through 5.37, USG FLEX series firmware versions 5.00 through 5.37, USG FLEX 50(W) series firmware versions 5.10 through 5.37, USG20(W)-VPN series firmware versions 5.10 through 5.37, and VPN series firmware versions 5.00 through 5.37, could allow an unauthenticated LAN-based attacker to store malicious scripts in a vulnerable device. A successful XSS attack could then result in the stored malicious scripts being executed to steal cookies when the user visits the specific CGI used for dumping ZTP logs.

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.2 CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected products

  • Zyxel ATP series firmware
  • Zyxel USG FLEX series firmware
  • Zyxel USG FLEX 50(W) series firmware
  • Zyxel USG20(W)-VPN series firmware
  • Zyxel VPN series firmware

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

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.