CVE-2025-24671: Pdfcrowd Save as PDF Object Injection

CVE-2025-24671 Overview

CVE-2025-24671 is a critical Insecure Deserialization vulnerability affecting the Pdfcrowd Save as PDF plugin for WordPress. The vulnerability allows attackers to perform PHP Object Injection attacks by exploiting improper handling of serialized data. This class of vulnerability (CWE-502: Deserialization of Untrusted Data) can lead to severe consequences including remote code execution, authentication bypass, and complete system compromise.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to potentially execute arbitrary code, manipulate application logic, or gain unauthorized access to WordPress installations running affected versions of the Save as PDF plugin by Pdfcrowd.

Affected Products

• Save as PDF plugin by Pdfcrowd versions up to and including 4.4.0
• WordPress installations using vulnerable plugin versions
• All configurations utilizing default plugin settings

Discovery Timeline

• 2025-01-27 - CVE CVE-2025-24671 published to NVD
• 2025-01-27 - Last updated in NVD database

Technical Details for CVE-2025-24671

Vulnerability Analysis

This vulnerability stems from the unsafe deserialization of user-controlled input within the Save as PDF plugin by Pdfcrowd. When WordPress processes requests handled by this plugin, serialized PHP data is deserialized without proper validation or sanitization. This allows an attacker to craft malicious serialized objects that, when deserialized, can trigger dangerous "magic methods" such as __wakeup(), __destruct(), or __toString() on existing PHP classes within the application context.

The attack surface is network-accessible and requires no authentication, meaning any remote attacker can attempt exploitation. The vulnerability affects the confidentiality, integrity, and availability of the target system, as successful exploitation can lead to arbitrary code execution with the privileges of the web server process.

Root Cause

The root cause of CVE-2025-24671 is the deserialization of untrusted data without implementing proper input validation or using safer data interchange formats. The plugin accepts serialized PHP data from user input and passes it directly to PHP's unserialize() function. This architectural flaw violates secure coding principles that mandate treating all external input as potentially malicious.

PHP Object Injection vulnerabilities occur when applications deserialize data from untrusted sources. Attackers can leverage Property-Oriented Programming (POP) chains—sequences of existing class methods that can be chained together through object properties—to achieve malicious outcomes ranging from file operations to command execution.

Attack Vector

The vulnerability is exploitable over the network without requiring any authentication or user interaction. An attacker would craft a malicious serialized PHP object containing a payload designed to exploit available POP gadgets within the WordPress ecosystem. This payload is then submitted to the vulnerable endpoint, where the plugin deserializes it.

Upon deserialization, PHP instantiates the attacker-controlled object and automatically invokes magic methods based on the object's lifecycle. If the WordPress installation or its plugins contain classes with exploitable magic methods, the attacker can chain these methods to achieve code execution or other malicious outcomes.

The exploitation process typically involves identifying usable gadget chains within the target environment, crafting a serialized payload that leverages these chains, and delivering the payload through the vulnerable input vector. Tools like PHPGGC (PHP Generic Gadget Chains) are commonly used by attackers to generate payloads for known WordPress and framework classes.

Detection Methods for CVE-2025-24671

Indicators of Compromise

• Unusual POST requests to WordPress endpoints associated with the Save as PDF plugin containing serialized PHP data patterns (base64-encoded or raw serialized strings starting with O:, a:, s:)
• Web server logs showing requests with abnormally long or obfuscated parameters to plugin-related URLs
• Unexpected file system changes, new files with execution permissions, or modified WordPress core files
• Anomalous outbound network connections from the web server process
• Error logs containing PHP deserialization warnings or unexpected class instantiation errors

Detection Strategies

• Deploy Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in request parameters, particularly looking for O:[0-9]+: regex patterns
• Implement file integrity monitoring on WordPress installations to detect unauthorized modifications to plugin files or core components
• Enable and monitor WordPress debug logging for deserialization errors or unexpected object instantiation
• Utilize SentinelOne Singularity Platform for endpoint detection of post-exploitation activities such as web shell deployment or suspicious process spawning from web server contexts

Monitoring Recommendations

• Monitor WordPress plugin directories for newly created or modified PHP files that could indicate web shell deployment
• Track process creation events originating from web server processes (Apache, Nginx, PHP-FPM) for anomalous child processes
• Implement network monitoring to detect unusual egress traffic patterns from WordPress hosting infrastructure
• Review access logs for reconnaissance patterns targeting known plugin endpoints

How to Mitigate CVE-2025-24671

Immediate Actions Required

• Update the Save as PDF plugin by Pdfcrowd to the latest patched version immediately
• If an update is not available, deactivate and remove the vulnerable plugin until a patch is released
• Conduct a security audit of WordPress installations to identify any signs of prior exploitation
• Review and restrict file system permissions for WordPress directories to limit potential post-exploitation impact
• Consider implementing additional security plugins that provide virtual patching capabilities

Patch Information

Organizations should check the Patchstack Vulnerability Advisory for the latest patch status and remediation guidance. Update to a version higher than 4.4.0 when available from the plugin vendor or WordPress plugin repository.

Workarounds

• Disable the Save as PDF plugin by Pdfcrowd until a security patch is available by navigating to WordPress Admin → Plugins and deactivating the plugin
• Implement WAF rules to block requests containing serialized PHP object patterns targeting plugin endpoints
• Restrict access to WordPress administrative and plugin endpoints using IP-based access controls where feasible
• Deploy virtual patching through security solutions like Wordfence or Patchstack that can block exploitation attempts at the application layer

# WordPress CLI command to deactivate vulnerable plugin
wp plugin deactivate save-as-pdf-by-pdfcrowd --path=/var/www/html/wordpress

# Verify plugin status
wp plugin status save-as-pdf-by-pdfcrowd --path=/var/www/html/wordpress

# Check for available updates
wp plugin update save-as-pdf-by-pdfcrowd --path=/var/www/html/wordpress