CVE-2026-41661 Admidio: Reflected XSS in msg_window.php via Square Bracket to HTML Tag Conversion
Unauthenticated attackers can execute arbitrary JavaScript in user browsers via reflected XSS in Admidio's message window endpoint.
- 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
- Available
What is CVE-2026-41661?
CVE-2026-41661 is a medium-severity cross-site scripting vulnerability in admidio, published on 7 May 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
Admidio is an open-source user management solution. Prior to version 5.0.9, an unauthenticated attacker can execute arbitrary JavaScript in any Admidio user's browser through a reflected XSS in system/msg_window.php. The endpoint passes user input through htmlspecialchars(), which does not encode square brackets. A subsequent call to Language::prepareTextPlaceholders() converts those brackets into HTML angle brackets, producing executable markup. This issue has been patched in version 5.0.9.
Weakness: CWE-79
Which versions are affected by CVE-2026-41661?
2 open source packages ship an affected version, including admidio/admidio.
| Package | Affected | Fixed in |
|---|---|---|
admidio/admidio Packagist | All versions | 5.0.9 |
admidio/admidio Packagist | All versions | 5.0.9 |
How do I fix CVE-2026-41661?
Upgrade admidio/admidio to 5.0.9 or later.
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-2026-41661 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-41661 exists.
Sources
Also known as GHSA-gq27-fc8w-vcmp.