CVE-2023-35139 Cross-site scripting in USG FLEX 50(W) series firmware

Medium 5.2 Published 28 Nov 2023 Updated 2 Aug 2024

An unauthenticated LAN attacker can inject malicious scripts into Zyxel firewall firmware, stealing user cookies upon visiting a specific log page.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2023-35139?

CVE-2023-35139 is a medium-severity cross-site scripting vulnerability in Zyxel USG FLEX 50(W) series firmware, published on 28 Nov 2023. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-79

Which versions are affected by CVE-2023-35139?

It affects 1 product.

Products include Zyxel Zld.

How do I fix CVE-2023-35139?

No fix has been published for CVE-2023-35139 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2023-35139 being exploited?

There is no known exploitation of CVE-2023-35139 in the wild and no public exploit code.

Sources

Also known as GHSA-wjqc-5477-jpgg.