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

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-26 · updated 2026-06-17
• Weakness: CWE-770

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.

Affected products

• Stirling Pdf: from 2.1.5 before 2.5.2 — fixed in 2.5.2

How to fix

Upgrade to a fixed version: Stirling Pdf 2.5.2. Check the vendor advisory for mitigations.

References

• https://github.com/Stirling-Tools/Stirling-PDF/security/advisories/GHSA-3932-2rfq-87xm
• https://github.com/Stirling-Tools/Stirling-PDF/security/advisories/GHSA-3932-2rfq-87xm

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