CVE-2025-3439: Everest Forms Plugin RCE Vulnerability

CVE-2025-3439 Overview

CVE-2025-3439 is a critical PHP Object Injection vulnerability affecting the Everest Forms plugin for WordPress, a popular form builder used for contact forms, quizzes, surveys, newsletters, and payment forms. The vulnerability exists in all versions up to and including 3.1.1 and stems from insecure deserialization of untrusted input via the field_value parameter.

This insecure deserialization flaw allows unauthenticated attackers to inject arbitrary PHP objects into the application. While no known Property-Oriented Programming (POP) chain exists within the Everest Forms plugin itself, the presence of a POP chain in any other installed plugin or theme could enable attackers to escalate the impact significantly—potentially leading to arbitrary file deletion, sensitive data retrieval, or remote code execution.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to potentially achieve remote code execution, delete arbitrary files, or steal sensitive data when combined with a POP chain from another WordPress component.

Affected Products

• Everest Forms WordPress Plugin versions up to and including 3.1.1
• WordPress sites running vulnerable Everest Forms versions with additional plugins/themes containing POP chains

Discovery Timeline

• 2025-04-11 - CVE-2025-3439 published to NVD
• 2025-04-23 - Last updated in NVD database

Technical Details for CVE-2025-3439

Vulnerability Analysis

This vulnerability falls under CWE-502 (Deserialization of Untrusted Data), a well-documented class of security issues that occurs when an application deserializes user-controlled input without proper validation. In the context of Everest Forms, the field_value parameter accepts serialized PHP data that is processed without adequate sanitization.

PHP Object Injection vulnerabilities are particularly dangerous in WordPress environments due to the extensive plugin ecosystem. While the Everest Forms plugin itself may not contain exploitable gadget chains, WordPress sites commonly run dozens of plugins and themes—any of which could provide the necessary POP chain to weaponize this deserialization flaw.

The attack is network-accessible and requires no authentication or user interaction, making it highly exploitable in real-world scenarios. An attacker can craft a malicious serialized payload targeting known POP chains from common WordPress plugins to achieve various malicious outcomes.

Root Cause

The root cause of this vulnerability is the unsafe use of PHP's unserialize() function on user-controlled input from the field_value parameter. The vulnerable code path can be traced to the admin entries view handler at includes/admin/views/html-admin-page-entries-view.php. When processing form entry data, the application deserializes field values without implementing proper input validation or using safer alternatives like JSON encoding.

Attack Vector

The attack leverages the network-accessible form processing functionality of the Everest Forms plugin. An unauthenticated attacker can submit a crafted request containing a malicious serialized PHP object in the field_value parameter. The exploitation flow follows these stages:

1. Reconnaissance: Attacker identifies WordPress sites running vulnerable Everest Forms versions
2. POP Chain Discovery: Attacker determines if additional plugins/themes with known POP chains are installed
3. Payload Crafting: Attacker constructs a serialized PHP object exploiting the identified POP chain
4. Exploitation: Malicious payload is submitted via the field_value parameter
5. Impact: Upon deserialization, the injected object triggers the POP chain, executing attacker-controlled actions

The vulnerability manifests in the form entry processing functionality where serialized data from the field_value parameter is deserialized without validation. For technical implementation details, see the WordPress Plugin Code Review and the Wordfence Vulnerability Intelligence report.

Detection Methods for CVE-2025-3439

Indicators of Compromise

• Unusual HTTP POST requests to Everest Forms endpoints containing serialized PHP data (look for O: or a: patterns in field_value parameters)
• Unexpected file modifications or deletions on the WordPress installation
• Anomalous PHP error logs referencing deserialization or object instantiation failures
• Suspicious outbound connections from the web server following form submissions

Detection Strategies

• Deploy web application firewall (WAF) rules to detect and block serialized PHP objects in POST parameters
• Implement file integrity monitoring to detect unauthorized modifications to WordPress core, plugin, and theme files
• Monitor PHP error logs for deserialization-related warnings or fatal errors
• Review server access logs for requests containing common PHP serialization patterns targeting Everest Forms endpoints

Monitoring Recommendations

• Enable verbose logging for the Everest Forms plugin to capture detailed request data
• Configure real-time alerting for file system changes within the WordPress installation directory
• Implement network-level monitoring for unusual data exfiltration patterns originating from the web server
• Regularly audit installed WordPress plugins and themes for known POP chains that could amplify this vulnerability

How to Mitigate CVE-2025-3439

Immediate Actions Required

• Update Everest Forms to a patched version immediately (versions after 3.1.1)
• Audit all installed WordPress plugins and themes to identify potential POP chain sources
• Review server logs for signs of exploitation attempts targeting the field_value parameter
• Implement WAF rules to block serialized PHP object patterns in form submissions

Patch Information

WPEverest has released a security patch addressing this vulnerability. The fix is available in the WordPress Changeset Update. The patch implements proper input validation to prevent untrusted data from being deserialized.

To update:

1. Navigate to Plugins → Installed Plugins in your WordPress admin panel
2. Locate Everest Forms and click "Update Now"
3. Verify the updated version is greater than 3.1.1
4. Clear any caching layers after the update

Workarounds

• If immediate patching is not possible, temporarily disable the Everest Forms plugin until an update can be applied
• Implement a WAF rule to filter requests containing serialized PHP objects in POST data
• Remove or disable any non-essential plugins and themes to reduce available POP chains
• Restrict access to form endpoints using server-level access controls while awaiting patch deployment

# Example WAF rule for ModSecurity to block PHP serialization patterns
SecRule ARGS "@rx [Oo]:[0-9]+:\"" \
    "id:100001,\
    phase:2,\
    deny,\
    status:403,\
    msg:'Blocked PHP serialized object in request',\
    tag:'CVE-2025-3439'"