CVE-2026-42548 Flight: Reflected XSS via unvalidated JSONP callback in Flight::jsonp()
Attackers can execute arbitrary JavaScript in the victim's browser via unvalidated JSONP callback parameters in the Flight PHP framework.
- 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-2026-42548?
CVE-2026-42548 is a high-severity cross-site scripting vulnerability in flightphp core, published on 13 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
Flight is an extensible micro-framework for PHP. Prior to 3.18.1, Flight::jsonp() concatenates the ?jsonp= query parameter directly into an application/javascript response body without validating that the value is a legal JavaScript identifier. An attacker can inject arbitrary JavaScript that executes in the response origin, enabling reflected cross-site scripting. This vulnerability is fixed in 3.18.1.
Weakness: CWE-79
Which versions are affected by CVE-2026-42548?
2 open source packages ship an affected version, including flightphp/core.
| Package | Affected | Fixed in |
|---|---|---|
flightphp/core Packagist | All versions | 3.18.1 |
flightphp/core Packagist | All versions | 3.18.1 |
How do I fix CVE-2026-42548?
Upgrade flightphp/core to 3.18.1 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-2026-42548 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42548 exists.
Sources
Also known as GHSA-fcx8-ph5r-mxr4.