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CVE-2025-55150: SSRF Vulnerability in Stirling-PDF Web Application

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Overview

In today’s post, we delve into the intricacies of a critical vulnerability discovered in the Stirling-PDF web application, a widely used locally hosted application that performs various operations on PDF files. The vulnerability, identified as CVE-2025-55150, affects the application’s ability to securely convert HTML to PDF, potentially leading to system compromise or data leakage. As the vulnerability scores an 8.6 on CVSS Severity Score, understanding, detecting, and mitigating this risk is of paramount importance to prevent substantial damage to system integrity and confidentiality.

Vulnerability Summary

CVE ID: CVE-2025-55150
Severity: Critical (8.6 CVSS Score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

Stirling-PDF | Prior to 1.1.0

How the Exploit Works

The exploit leverages the /api/v1/convert/html/pdf endpoint in the Stirling-PDF application. When converting HTML to PDF, the backend makes a call to a third-party tool and includes a sanitizer for security sanitization. However, due to insufficient security measures in place, an attacker can bypass this sanitizer, leading to a Server Side Request Forgery (SSRF) vulnerability. This allows the attacker to make requests from the vulnerable server to internal resources that would otherwise be inaccessible, potentially leading to system compromise or data leakage.

Conceptual Example Code

Here’s a conceptual example of how the vulnerability might be exploited:

POST /api/v1/convert/html/pdf HTTP/1.1
Host: target.example.com
Content-Type: application/json
{
"html": "<img src='http://localhost:8080/internal_endpoint'>"
}

In this example, the attacker is using the HTML to PDF conversion feature to make an internal request, potentially accessing sensitive information or functionality.

Mitigation Guidance

Users of the affected Stirling-PDF versions are urged to apply the vendor patch provided in version 1.1.0 to guard against this vulnerability. As a temporary mitigation measure, users can deploy a Web Application Firewall (WAF) or Intrusion Detection System (IDS) to monitor and block potential SSRF attempts. However, the application of the vendor patch remains the most effective solution to this vulnerability.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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