CVE-2018-25324: Simple Fields WordPress Path Traversal

CVE-2018-25324 Overview

CVE-2018-25324 is a local file inclusion (LFI) vulnerability in the Simple Fields WordPress plugin versions 0.2 through 0.3.5. The plugin fails to validate the wp_abspath parameter in simple_fields.php, allowing unauthenticated attackers to inject null bytes and read arbitrary files on PHP versions before 5.3.4. Attackers can escalate the issue to remote code execution by poisoning Apache log files with PHP payloads and including them through the same parameter when allow_url_include is enabled. The flaw is categorized under CWE-98 (Improper Control of Filename for Include/Require Statement).

Critical Impact

Unauthenticated remote attackers can disclose sensitive system files such as /etc/passwd and potentially achieve remote code execution through log poisoning on legacy PHP deployments.

Affected Products

• Simple Fields WordPress Plugin version 0.2
• Simple Fields WordPress Plugin versions 0.3.x through 0.3.5
• PHP runtimes earlier than 5.3.4 hosting the plugin

Discovery Timeline

• 2026-05-17 - CVE-2018-25324 published to NVD
• 2026-05-18 - Last updated in NVD database

Technical Details for CVE-2018-25324

Vulnerability Analysis

The Simple Fields plugin uses the wp_abspath GET parameter inside simple_fields.php to construct an include path for loading WordPress bootstrap files. The plugin concatenates the attacker-controlled value directly into a PHP require or include call without sanitization or allowlisting. Because the file is reachable without authentication, any visitor can manipulate the path that PHP attempts to load.

On PHP versions earlier than 5.3.4, null byte (%00) injection truncates the included filename, stripping suffixes that the plugin appends. This lets attackers escape the expected .php boundary and target arbitrary files on the local filesystem. The vulnerability has an associated EPSS score of 0.019%, indicating a low predicted exploitation rate in the wild.

Root Cause

The root cause is missing input validation on the wp_abspath parameter. The plugin trusts user-supplied input to locate the WordPress installation root and never enforces an allowlist of acceptable paths or canonicalizes the value before passing it to a file inclusion sink.

Attack Vector

An unauthenticated attacker issues a crafted GET request to simple_fields.php with a wp_abspath value pointing to a target file followed by a null byte. PHP truncates the path at the null byte and loads the chosen file. To achieve code execution, an attacker first writes PHP code into the Apache access.log by sending a request with a malicious User-Agent header. The attacker then sets wp_abspath to the log path, causing the server to execute the embedded payload when allow_url_include permits remote includes. Technical proof-of-concept details are available in the Exploit-DB #44425 entry and the VulnCheck advisory.

Detection Methods for CVE-2018-25324

Indicators of Compromise

• Web server requests to simple_fields.php containing a wp_abspath query parameter with %00, ../, or absolute filesystem paths
• Apache or PHP error log entries referencing inclusion of /etc/passwd, /proc/self/environ, or access.log
• Unusual User-Agent strings containing PHP tags such as <?php recorded in web access logs

Detection Strategies

• Inspect HTTP request logs for the wp_abspath parameter and alert on values containing null bytes, directory traversal sequences, or non-WordPress paths
• Monitor PHP include and require operations that resolve to log files, /etc, /proc, or other system directories
• Audit WordPress plugin inventories for Simple Fields versions between 0.2 and 0.3.5 and flag any active installations

Monitoring Recommendations

• Enable web application firewall rules that block null byte sequences and traversal patterns in query strings targeting WordPress plugin endpoints
• Forward Apache, NGINX, and PHP-FPM logs to a centralized analytics platform and correlate file inclusion attempts with subsequent process activity
• Baseline outbound network connections from PHP worker processes and alert on anomalous shell or download behavior

How to Mitigate CVE-2018-25324

Immediate Actions Required

• Disable or uninstall the Simple Fields plugin on any WordPress site running versions 0.2 through 0.3.5
• Upgrade PHP to a supported release; PHP 5.3.4 and later neutralize null byte truncation in filesystem APIs
• Set allow_url_include = Off and allow_url_fopen = Off in php.ini to block remote include and log-poisoning chains

Patch Information

No vendor patch is referenced in the advisory data. The Simple Fields plugin has been removed from the WordPress plugin directory in its vulnerable form. Site operators should migrate to an actively maintained custom fields plugin and confirm the upgrade by reviewing the VulnCheck advisory.

Workarounds

• Block external access to simple_fields.php at the web server or WAF layer until the plugin is removed
• Restrict file permissions so the PHP worker cannot read sensitive files such as /etc/passwd or write to web-accessible log directories
• Relocate Apache access and error logs outside the document root and outside any path reachable through plugin includes

# Configuration example: harden php.ini against LFI-to-RCE chains
allow_url_include = Off
allow_url_fopen = Off
open_basedir = "/var/www/html:/tmp"
disable_functions = "exec,passthru,shell_exec,system,proc_open,popen"