CVE-2025-13773 Exploit & Vulnerability Analysis

1. Vulnerability Background

• What is this vulnerability?

  • CVE-2025-13773 is an unauthenticated remote code execution (RCE) vulnerability in the Print Invoice & Delivery Notes for WooCommerce WordPress plugin.
  • The root cause is a combination of insecure PDF generation configuration and missing access control / escaping in the plugin.
  • Specifically, Dompdf was configured with isPhpEnabled = true, allowing embedded PHP code inside the generated HTML to execute on the server.

• Why is it critical/important?

  • RCE is one of the highest-impact vulnerabilities for web applications.
  • An attacker can execute arbitrary PHP code with the privileges of the web server process.
  • This can lead to full site compromise, data exfiltration, credential theft, pivoting to other infrastructure, and persistent backdoors.

• What systems/versions are affected?

  • All versions of Print Invoice & Delivery Notes for WooCommerce up to and including 5.8.0.
  • The issue is present wherever the plugin uses Dompdf for PDF rendering and retains the insecure configuration.

2. Technical Details

• Root cause analysis

  • The core issue is insecure Dompdf configuration in includes/front/wcdn-front-function.php.
  • Old code:
    • options->set( 'isPhpEnabled', true );
  • With this option set, Dompdf evaluates PHP code found in HTML content during PDF generation.
  • This is unsafe when any of the rendered content may be influenced by user input.
  • The CVE description also identifies additional weaknesses:
    • missing capability check in WooCommerce_Delivery_Notes::update
    • missing output escaping in template.php
  • These weaknesses create an exploitable chain: unauthenticated access combined with injection of PHP-capable content into the PDF renderer.

• Attack vector and exploitation conditions

  • An attacker needs:
    • the vulnerable plugin installed,
    • access to a function or field that is included in the HTML sent to Dompdf,
    • the ability to trigger PDF generation or update the delivery note content.
  • The likely chain:
    1. The attacker injects PHP code into a user-controllable field or template variable.
    2. The plugin generates a delivery note/invoice PDF using Dompdf.
    3. Dompdf evaluates the embedded PHP code because isPhpEnabled is enabled.
    4. The injected PHP executes on the server.
  • The missing capability check means the attacker may not need to be authenticated to reach the vulnerable update path.

• Security implications

  • Arbitrary code execution on the web server.
  • Potential compromise of the WordPress site and host environment.
  • Ability to execute system commands, install backdoors, modify files, or exfiltrate data.
  • RCE via a plugin used in ecommerce sites is especially dangerous because it may include payment, customer, and order data.

3. Patch Analysis

• What code changes were made?

  • In includes/front/wcdn-front-function.php, the Dompdf option was changed from:
    • options->set( 'isPhpEnabled', true );
  • to:
    • options->set( 'isPhpEnabled', false );

• How do these changes fix the vulnerability?

  • Disabling isPhpEnabled prevents Dompdf from executing PHP embedded in HTML content.
  • Any injected <?php ... ?> payload is no longer evaluated by the PDF renderer.
  • This removes the code execution vector provided by Dompdf, which is the critical exploitation mechanism.

• Security improvements introduced

  • Changes the Dompdf configuration to a secure default.
  • Eliminates a dangerous capability that should never be enabled for untrusted content.
  • Reduces the attack surface of PDF generation in the plugin.
  • Note: while this fix addresses the Dompdf vector, the broader issue also requires proper authorization checks and escaping elsewhere in the plugin.

4. Proof of Concept (PoC) Guide

• Prerequisites for exploitation

  • WordPress site running Print Invoice & Delivery Notes for WooCommerce version 5.8.0 or earlier.
  • Plugin uses Dompdf for PDF generation.
  • Attacker can influence content that is rendered in the delivery note or invoice HTML.
  • Vulnerable path accessible without sufficient authorization (as indicated by the missing capability check).

• Step-by-step exploitation approach

  1. Identify a field or template variable included in generated PDF output.
  2. Inject PHP code, e.g.:
     • <?php system($_GET['cmd']); ?>
  3. Trigger the plugin’s PDF generation routine for an invoice or delivery note.
  4. Access the generated PDF endpoint with a command parameter, for example:
     • ?cmd=id
  5. Observe the command output or side effects in the response or server behavior.

• Expected behavior vs exploited behavior

  • Expected behavior:
    • The plugin generates a PDF from HTML content and returns a delivery note or invoice PDF.
    • No server-side PHP execution occurs from user-supplied content.
  • Exploited behavior:
    • The injected PHP payload is executed during PDF generation.
    • Arbitrary commands run on the server as the web server user.

• How to verify the vulnerability exists

  • Confirm plugin version is <= 5.8.0.
  • Inspect includes/front/wcdn-front-function.php and verify isPhpEnabled is set to true.
  • Test whether user-controlled content appears in the rendered PDF HTML.
  • Attempt a non-destructive probe payload and observe whether PHP execution occurs.

5. Recommendations

• Mitigation strategies

  • Upgrade the plugin to a patched version where isPhpEnabled is disabled.
  • If patching immediately is not possible, disable or remove the affected PDF generation functionality.
  • Restrict access to plugin endpoints with proper capability checks and authentication.

• Detection methods

  • Monitor web logs for requests containing PHP tags (<?php) to plugin endpoints.
  • Look for unusual POSTs/GETs targeting delivery note or update routes.
  • Audit plugin files for insecure Dompdf configuration and missing access controls.
  • Use host-based detection for unexpected PHP execution from the plugin process.

• Best practices to prevent similar issues

  • Never enable PHP execution in template or rendering engines for untrusted content.
  • Apply least privilege to all admin/update functions: verify capabilities before performing updates.
  • Escape all output in templates and avoid rendering raw user input.
  • Use secure default settings for third-party libraries.
  • Perform regular code reviews of plugin modules that handle rich content and file generation.