CVE-2026-33436 Stirling-PDF: Reflected XSS through crafted filename in file upload functionality

Low 3.1 Published 17 Apr 2026 Updated 20 Apr 2026

Attackers can execute arbitrary JavaScript in victim browsers via crafted filenames in Stirling-PDF uploads, potentially leading to session hijacking.

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-2026-33436?

CVE-2026-33436 is a low-severity cross-site scripting vulnerability in Stirling-Tools Stirling-PDF, published on 17 Apr 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

Stirling-PDF is a locally hosted web application that facilitates various operations on PDF files. In versions prior to 2.0.0, file upload endpoints render user-supplied filenames directly into HTML using unsafe methods like innerHTML without sanitization. An attacker can craft a file with a malicious filename containing JavaScript that executes in the uploading user's browser context, resulting in reflected XSS. The issue affects numerous upload endpoints across the application. The issue has been fixed in version 2.0.0.

Weakness: CWE-79, CWE-20, CWE-116

Which versions are affected by CVE-2026-33436?

It affects 1 product.

Products include Stirlingpdf Stirling Pdf.

How do I fix CVE-2026-33436?

No fix has been published for CVE-2026-33436 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-2026-33436 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33436 exists.

Sources

Also known as GHSA-q5j3-4m5w-wp75.