CVE-2026-46392 HAX CMS PHP Has a Stored XSS via Case-Sensitivity Mismatch in HTML Upload Validation
Attackers can execute arbitrary JavaScript in the victim's browser by uploading HTML files with uppercase extensions that bypass content-disposition headers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-46392?
CVE-2026-46392 is a high-severity cross-site scripting vulnerability in haxtheweb haxcms-php, published on 5 Jun 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
HAX CMS helps manage microsite universe with PHP or NodeJs backends. Prior to version 26.0.0 of HAX CMS PHP, the `saveFile` endpoint validates upload extensions case-insensitively and writes the filename to disk verbatim, but the `.htaccess` rule that forces `Content-Disposition: attachment` on HTML files is case-sensitive. An HTML file uploaded with an uppercase extension (`.HTML`, `.Html`, `.HTM`) is still served as `text/html` but the forced-download header never applies, so the browser renders it inline and executes any embedded JavaScript in the HAXcms origin. This bypasses the mitigation shipped for CVE-2026-22704. Version 26.0.0 contains a fix.
Which versions are affected by CVE-2026-46392?
How do I fix CVE-2026-46392?
No fix has been published for CVE-2026-46392 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-2026-46392 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-46392 exists.