CVE-2026-1540: Spam Protect Contact Form 7 RCE Flaw

CVE-2026-1540 Overview

CVE-2026-1540 is a code injection vulnerability affecting the Spam Protect for Contact Form 7 WordPress plugin before version 1.2.10. The vulnerability allows logging to a PHP file, which could enable an attacker with editor-level access to achieve Remote Code Execution (RCE) by using a crafted header. This vulnerability is classified under CWE-94 (Improper Control of Generation of Code).

Critical Impact

Authenticated attackers with editor privileges can execute arbitrary PHP code on vulnerable WordPress installations, potentially leading to complete site compromise, data theft, and malware distribution.

Affected Products

• Spam Protect for Contact Form 7 WordPress plugin versions prior to 1.2.10
• WordPress installations using vulnerable plugin versions
• Web servers hosting affected WordPress instances

Discovery Timeline

• April 2, 2026 - CVE-2026-1540 published to NVD
• April 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1540

Vulnerability Analysis

This vulnerability stems from improper handling of log file generation within the Spam Protect for Contact Form 7 plugin. The plugin writes log data to a file with a .php extension, and fails to properly sanitize header content before logging. When an attacker with editor access crafts a malicious header containing PHP code, that code is written directly to the log file. Since the log file has a PHP extension and resides within the web-accessible directory structure, the attacker can then request this file via HTTP, causing the injected PHP code to execute on the server.

The attack requires authenticated access with at least editor-level privileges, which limits the attack surface to insiders or attackers who have compromised an editor account. However, once exploited, the vulnerability provides complete server-side code execution capabilities.

Root Cause

The root cause is the combination of two insecure design decisions: using a PHP file extension for log files and failing to sanitize user-controllable input before writing it to the log. The logging functionality does not properly escape or filter header values, allowing PHP code injection. Additionally, storing logs in a web-accessible location with an executable extension means the web server will process any PHP code contained within the file when accessed.

Attack Vector

The attack is network-based and requires authentication with editor privileges. An attacker must first gain access to a WordPress account with editor-level permissions. Once authenticated, the attacker can manipulate request headers to inject PHP code that gets written to the plugin's log file. The attacker then accesses the log file directly via a web request, triggering execution of the injected code.

The exploitation mechanism involves sending requests to the WordPress site with specially crafted headers containing PHP code payloads. The vulnerable logging function captures these headers and writes them verbatim to the PHP log file. Since no sanitization occurs, the malicious PHP code is preserved intact and becomes executable when the log file is subsequently requested through the web server.

Detection Methods for CVE-2026-1540

Indicators of Compromise

• Unusual PHP files in plugin directories with recent modification timestamps
• Log files containing PHP code patterns such as <?php, eval(, system(, or base64_decode(
• Unexpected outbound network connections from the web server process
• Web access logs showing direct requests to plugin log files

Detection Strategies

• Monitor WordPress plugin directories for newly created or modified PHP files
• Implement file integrity monitoring on the /wp-content/plugins/ directory tree
• Review web server access logs for requests to unusual file paths within plugin directories
• Deploy web application firewall rules to detect PHP code patterns in HTTP headers

Monitoring Recommendations

• Enable verbose logging for WordPress authentication events to track editor-level access
• Configure alerts for PHP file creation or modification in plugin directories
• Implement real-time log analysis to detect PHP code injection patterns in header values
• Monitor for process spawning from web server processes that may indicate code execution

How to Mitigate CVE-2026-1540

Immediate Actions Required

• Update Spam Protect for Contact Form 7 plugin to version 1.2.10 or later immediately
• Audit WordPress user accounts and remove unnecessary editor-level privileges
• Review plugin log files for any evidence of PHP code injection
• Consider temporarily disabling the plugin until the update can be applied

Patch Information

The vulnerability is fixed in Spam Protect for Contact Form 7 version 1.2.10. Administrators should update to this version or later through the WordPress plugin management interface or by manually downloading the patched version. For detailed information about this vulnerability, refer to the WPScan Vulnerability Advisory.

Workarounds

• Restrict editor-level access to trusted users only until patching is complete
• Configure web server rules to block direct access to plugin log files
• Implement additional input validation at the web server level for HTTP headers
• Consider using a web application firewall to filter requests containing PHP code patterns

# Apache configuration to block direct access to plugin log files
<Directory "/var/www/html/wp-content/plugins/spam-protect-for-contact-form-7">
    <FilesMatch "\.(log|php\.log)$">
        Require all denied
    </FilesMatch>
</Directory>