How severe is CVE-2023-35139?

CVE-2023-35139 has a CVSS 3.x base score of 5.2, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2023-35139 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-35139?

CVE-2023-35139 affects Zyxel Zld. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2023-35139?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-35139 published?

CVE-2023-35139 was published on 2023-11-28 and last updated on 2026-06-17.

CVE-2023-35139

CVE-2023-35139 is a medium-severity vulnerability in Zyxel Zld with a CVSS 3.x base score of 5.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.2)
EPSS exploit prediction: 0% (37th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Zyxel Zld
Published: 2023-11-28
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2023-35139?: 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.
How severe is CVE-2023-35139?: CVE-2023-35139 has a CVSS 3.x base score of 5.2, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2023-35139 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-35139?: CVE-2023-35139 affects Zyxel Zld. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-35139?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-35139 published?: CVE-2023-35139 was published on 2023-11-28 and last updated on 2026-06-17.

References

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-aps

Affected products (1)

cpe:2.3:o:zyxel:zld:*:*:*:*:*:*:*:*

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