CVE-2026-3990 CesiumGS CesiumJS standalone.html cross site scripting
Cross-site scripting in CesiumJS Sandcastle demo allows remote attackers to execute arbitrary scripts via the c argument.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-3990?
CVE-2026-3990 is a medium-severity cross-site scripting vulnerability in CesiumGS CesiumJS, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
A security flaw has been discovered in CesiumGS CesiumJS up to 1.137.0. Affected by this issue is some unknown functionality of the file Apps/Sandcastle/standalone.html. The manipulation of the argument c results in cross site scripting. The attack can be launched remotely. The exploit has been released to the public and may be used for attacks. The presence of this vulnerability remains uncertain at this time. The vendor was contacted early about this disclosure but did not respond in any way. According to CVE-2023-48094, "the vendor's position is that Apps/Sandcastle/standalone.html is part of the CesiumGS/cesium GitHub repository, but is demo code that is not part of the CesiumJS JavaScript library product."
Which versions are affected by CVE-2026-3990?
How do I fix CVE-2026-3990?
No fix has been published for CVE-2026-3990 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-2026-3990 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-3990 exists.
Sources
Also known as GHSA-pf42-2vwp-g7x9.