CVE-2026-33438 Stirling-PDF vulnerable to DoS via add-watermark

Medium 6.5 Published 26 Mar 2026 Updated 26 Mar 2026

Authenticated attackers can crash Stirling-PDF servers by submitting extreme parameter values to the add-watermark endpoint.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-33438?

CVE-2026-33438 is a medium-severity denial of service vulnerability in Stirling-Tools Stirling-PDF, published on 26 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Stirling-PDF is a locally hosted web application that allows you to perform various operations on PDF files. Versions starting in 2.1.5 and prior to 2.5.2 have Denial of Service (DoS) vulnerability in the Stirling-PDF watermark functionality (`/api/v1/security/add-watermark` endpoint). The vulnerability allows authenticated users to cause resource exhaustion and server crashes by providing extreme values for the `fontSize` and `widthSpacer` parameters. Version 2.5.2 patches the issue.

Weakness: CWE-770

Which versions are affected by CVE-2026-33438?

It affects 1 product.

Products include Stirling Stirling Pdf.

How do I fix CVE-2026-33438?

No fix has been published for CVE-2026-33438 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-33438 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33438 exists.

Sources

Also known as GHSA-3932-2rfq-87xm.