CVE-2025-56589: Apryse HTML2PDF SDK SSRF Vulnerability

CVE-2025-56589 Overview

A Local File Inclusion (LFI) and Server-Side Request Forgery (SSRF) vulnerability was discovered in the InsertFromHtmlString() function of the Apryse HTML2PDF SDK through version 11.6.0. These vulnerabilities could allow an attacker to read local files on the server or make arbitrary HTTP requests to internal or external services. Both vulnerabilities could lead to the disclosure of sensitive data or potential system takeover.

Critical Impact

Attackers can exploit these vulnerabilities to access sensitive local files and make unauthorized requests to internal services, potentially leading to full system compromise or data exfiltration.

Affected Products

• Apryse HTML2PDF SDK versions through 11.6.0
• Applications utilizing the InsertFromHtmlString() function
• Web services that process user-supplied HTML content through the SDK

Discovery Timeline

• 2026-01-22 - CVE CVE-2025-56589 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2025-56589

Vulnerability Analysis

This vulnerability combines two dangerous security flaws in the Apryse HTML2PDF SDK's HTML processing functionality. The InsertFromHtmlString() function fails to properly sanitize and validate HTML input before processing it, allowing attackers to inject malicious payloads that trigger both Local File Inclusion and Server-Side Request Forgery attacks.

The LFI component enables attackers to read arbitrary files from the server's filesystem by manipulating HTML elements to reference local file paths. The SSRF component allows attackers to craft HTML content that causes the server to make requests to arbitrary internal or external URLs, potentially accessing internal services that are otherwise protected from external access.

When HTML content is passed to the vulnerable function, the SDK processes embedded resources (such as images, stylesheets, or iframes) without adequately validating their source URLs. This lack of validation allows attackers to specify file:// protocol handlers for LFI attacks or internal network addresses for SSRF attacks.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and URL scheme filtering within the InsertFromHtmlString() function. The function processes HTML content and resolves external resources without properly restricting allowed protocols (such as file://, http://, https://) or validating destination URLs against allowlists. This allows malicious actors to leverage the HTML-to-PDF conversion process as a proxy to access restricted resources.

Attack Vector

An attacker can exploit these vulnerabilities by submitting crafted HTML content to any application that uses the Apryse HTML2PDF SDK's InsertFromHtmlString() function. For the LFI attack, the attacker embeds HTML elements with file:// protocol references to sensitive files such as /etc/passwd, configuration files, or application secrets. For the SSRF attack, the attacker includes references to internal network resources or cloud metadata endpoints (e.g., http://169.254.169.254/).

The attack is particularly dangerous in scenarios where applications accept user-supplied HTML for PDF generation, such as invoice generators, report builders, or document conversion services. The vulnerability does not require authentication to exploit if the affected function processes untrusted input.

For technical details on exploitation techniques, refer to the Stratascale SSRF & LFI Analysis.

Detection Methods for CVE-2025-56589

Indicators of Compromise

• Unexpected file access attempts to sensitive system files such as /etc/passwd, /etc/shadow, or application configuration files
• Outbound HTTP requests from the PDF generation service to internal IP ranges (10.x.x.x, 172.16.x.x, 192.168.x.x) or cloud metadata endpoints
• Log entries showing file:// protocol references in HTML content submitted for PDF conversion
• Anomalous network traffic from application servers to internal services that should not be accessible

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block HTML content containing file:// protocol handlers or internal IP addresses
• Monitor application logs for HTML content containing suspicious URL schemes or references to sensitive file paths
• Deploy network-level monitoring to detect unusual outbound connections from PDF processing services to internal network segments
• Use endpoint detection and response (EDR) solutions to monitor file access patterns on servers running the Apryse SDK

Monitoring Recommendations

• Enable verbose logging for the HTML2PDF conversion process to capture all resource loading attempts
• Configure network segmentation alerts for traffic originating from PDF processing services to restricted internal networks
• Implement file integrity monitoring on servers hosting the Apryse SDK to detect unauthorized file access
• Set up alerts for cloud metadata endpoint access attempts from application servers

How to Mitigate CVE-2025-56589

Immediate Actions Required

• Audit all applications using the Apryse HTML2PDF SDK to identify instances of the vulnerable InsertFromHtmlString() function
• Implement strict input validation to sanitize HTML content before processing, removing or blocking dangerous URL schemes
• Configure network-level controls to prevent outbound connections from PDF processing services to internal networks and cloud metadata endpoints
• Consider isolating PDF generation services in sandboxed environments with restricted file system and network access

Patch Information

Check the Apryse Official Website for the latest security updates and patched versions of the HTML2PDF SDK. Organizations should upgrade to a version that addresses these vulnerabilities as soon as patches become available.

Workarounds

• Implement a URL allowlist that permits only https:// protocol and approved external domains in HTML content processing
• Use content security policies to restrict resource loading during PDF generation to trusted sources only
• Deploy the PDF generation service in an isolated network segment with no access to internal resources or cloud metadata endpoints
• Consider using alternative HTML sanitization libraries to pre-process content before passing it to the SDK

# Example network segmentation configuration using iptables
# Block outbound access to internal networks from PDF processing service
iptables -A OUTPUT -m owner --uid-owner pdf-service -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -m owner --uid-owner pdf-service -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -m owner --uid-owner pdf-service -d 192.168.0.0/16 -j DROP
iptables -A OUTPUT -m owner --uid-owner pdf-service -d 169.254.169.254 -j DROP