CVE-2026-3300: Everest Forms Pro WordPress RCE Vulnerability

CVE-2026-3300 Overview

The Everest Forms Pro plugin for WordPress contains a critical Remote Code Execution vulnerability via PHP Code Injection affecting all versions up to and including 1.9.12. This vulnerability exists in the Calculation Addon's process_filter() function, which concatenates user-submitted form field values into a PHP code string without proper escaping before passing it to eval(). The sanitize_text_field() function applied to input does not escape single quotes or other PHP code context characters, enabling unauthenticated attackers to inject and execute arbitrary PHP code on the server.

Critical Impact

Unauthenticated attackers can achieve complete server compromise by injecting malicious PHP code through any string-type form field (text, email, URL, select, radio) when a form uses the "Complex Calculation" feature.

Affected Products

• Everest Forms Pro plugin for WordPress versions up to and including 1.9.12
• WordPress sites using the Complex Calculation feature in forms
• Any deployment utilizing the Calculation Addon functionality

Discovery Timeline

• 2026-03-31 - CVE-2026-3300 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-3300

Vulnerability Analysis

This PHP Code Injection vulnerability (CWE-94) allows unauthenticated remote attackers to execute arbitrary code on affected WordPress installations. The vulnerability stems from unsafe use of PHP's eval() function combined with inadequate input sanitization. When a form administrator configures the "Complex Calculation" feature, the plugin processes user-submitted field values by concatenating them directly into a PHP expression string. This string is then passed to eval() for dynamic calculation execution.

The core issue is that sanitize_text_field(), the WordPress function used for input sanitization, does not escape characters that have special meaning in PHP string contexts—most notably single quotes. This allows attackers to break out of the string context and inject arbitrary PHP statements that will be executed by the eval() call.

Root Cause

The root cause is the dangerous combination of unsanitized user input with PHP's eval() function in the process_filter() function. The sanitize_text_field() WordPress sanitization function is designed for display purposes and does not provide adequate protection against code injection attacks. It fails to escape single quotes, backslashes, and other characters that can terminate string literals and introduce new PHP code. This architectural flaw allows user-controlled data to directly influence executed code.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker identifies a WordPress site running Everest Forms Pro with the Complex Calculation feature enabled on any public-facing form. By submitting a crafted payload containing PHP code injection syntax through any string-type form field (text, email, URL, select, or radio), the malicious input is processed by process_filter() and executed via eval(). This grants the attacker the ability to execute arbitrary PHP code with the web server's privileges, potentially leading to full server compromise, data exfiltration, or lateral movement within the hosting environment.

The vulnerability mechanism involves injecting single quotes to escape the string context, followed by arbitrary PHP statements. When the process_filter() function builds the calculation expression and passes it to eval(), the injected code executes on the server. For detailed technical analysis, refer to the WordPress Plugin Code Review and the Wordfence Vulnerability Report.

Detection Methods for CVE-2026-3300

Indicators of Compromise

• Unusual PHP process spawning or system command execution originating from web server processes
• Unexpected outbound network connections from WordPress application servers
• Web server access logs showing suspicious form submissions with encoded or escaped special characters
• New or modified PHP files appearing in WordPress directories without administrative action
• Evidence of webshell deployment or backdoor installation

Detection Strategies

• Monitor web application logs for form submissions containing PHP syntax elements such as single quotes followed by semicolons, function calls, or variable assignments
• Implement Web Application Firewall (WAF) rules to detect and block PHP code patterns in POST request parameters
• Deploy file integrity monitoring on WordPress installations to detect unauthorized file modifications
• Analyze server-side process execution for anomalous child processes spawned by PHP/Apache/Nginx

Monitoring Recommendations

• Enable detailed logging for WordPress form plugin activities and review submission data for anomalous patterns
• Configure SIEM alerts for suspicious PHP execution patterns or unusual outbound connections from web servers
• Implement endpoint detection and response (EDR) solutions to monitor for post-exploitation activity
• Establish baseline behavior for legitimate form submissions to identify statistical anomalies

How to Mitigate CVE-2026-3300

Immediate Actions Required

• Update Everest Forms Pro plugin to a patched version immediately if available (check the Everest Forms Changelog for security updates)
• Disable the Complex Calculation feature on all forms until a patch is applied
• Consider temporarily deactivating the Everest Forms Pro plugin on production sites if updates are not available
• Review server access logs for evidence of prior exploitation attempts

Patch Information

Organizations should monitor the Everest Forms Changelog for security patches addressing this vulnerability. The Wordfence Vulnerability Report provides additional details on affected versions and remediation guidance. Until an official patch is released, the following workarounds should be implemented to reduce risk exposure.

Workarounds

• Disable the Complex Calculation feature in all Everest Forms Pro forms to eliminate the vulnerable code path
• Implement WAF rules to block form submissions containing PHP code injection patterns (single quotes, eval, exec, system, passthru)
• Restrict form access to authenticated users only where business requirements allow
• Consider using alternative form plugins without dynamic calculation features until a patch is available

# Example WAF rule to block suspicious PHP patterns in form submissions
# ModSecurity rule example for Apache/Nginx
SecRule ARGS "@rx ('\s*;|\beval\b|\bexec\b|\bsystem\b|\bpassthru\b)" \
    "id:1001,phase:2,deny,status:403,msg:'Potential PHP injection attempt blocked'"