CVE-2026-6455: WP Contact Form 7 DB Handler CSRF & SQL Injection Leads to Arbitrary File Deletion

Technical summary

CVE-2026-6455 is a CSRF-enabled exploitation chain in WP Contact Form 7 DB Handler through version 3.0. The process_bulk_action() function lacks proper nonce verification—it only checks for a nonce if the _wpnonce field is present in the POST body, allowing attackers to bypass this protection entirely by omitting the field. This is combined with SQL injection via an unparameterized user-supplied ID value in a numeric SQL context (WHERE ID = $ID). The attacker crafts a UNION-based SQL injection payload using CHAR() functions to circumvent esc_sql() quote-escaping, causing the query to return a malicious serialized PHP object as post_content. When deserialized, array keys containing 'ys_cfdbh_file' trigger unsafe file operations: values are appended to the WordPress uploads directory without path traversal validation and passed directly to wp_delete_file(), enabling deletion of arbitrary files including wp-config.php and other system-critical files.

Business impact

Successful exploitation could result in complete website defacement or destruction. Deletion of wp-config.php breaks database connectivity and WordPress functionality entirely. Attackers could also remove backup files, security plugins, or audit logs, complicating incident response and recovery. Organizations running this plugin should assume that a compromised or social-engineered administrator account—or any administrator visiting an attacker-controlled page—puts the entire WordPress installation at risk of irreversible data loss and operational downtime.

Affected systems

WP Contact Form 7 DB Handler plugin for WordPress, versions up to and including 3.0, is affected. Any WordPress installation with this plugin active and an administrator user represents an attack surface. The vulnerability requires administrator access via CSRF; attackers cannot directly interact with the vulnerable functions without an authenticated user's browser session.

Exploitability

Exploitability is moderate-to-high in targeted scenarios. The attack requires social engineering (tricking an administrator into visiting a malicious page) but no authentication from the attacker's own account. Once triggered, exploitation is reliable: the CSRF payload is straightforward, SQL injection via numeric context is predictable, and PHP deserialization of controlled data is deterministic. The lack of any network restrictions (AV:N/AC:L) and the design flaw allowing nonce bypass (omitting the field entirely) make this trivial to weaponize. However, it does require user interaction (UI:R)—an administrator must visit the attacker's page or click a malicious link.

Remediation

Patch to a version newer than 3.0 as soon as available from the plugin vendor. Verify the patch addresses (1) mandatory nonce verification that cannot be bypassed by field omission, (2) parameterized SQL queries using prepare() or equivalent, and (3) removal of unsafe deserialization or strict validation of serialized data structures. Until patching is complete, disable the WP Contact Form 7 DB Handler plugin or restrict administrative access to trusted users and networks only.

Patch guidance

Contact the plugin vendor or check the WordPress Plugin Directory for an updated version addressing this vulnerability. When an update is released, verify the changelog explicitly mentions CSRF protection, SQL injection fixes, and safe deserialization practices. Apply updates to all WordPress environments running this plugin. Test thoroughly in a staging environment first, as this plugin manages contact form data; ensure no data loss occurs during or after the update.

Detection guidance

Monitor web server logs and WordPress debug logs for POST requests to the plugin's admin-ajax.php endpoint containing bulk action payloads without a _wpnonce parameter. Watch for database query errors or unusual UNION-based SQL patterns in WordPress debug.log. File integrity monitoring (FIM) on wp-config.php and other critical files will alert to unauthorized deletions. Check WordPress audit logs or security plugins for unexpected administrative actions. Implement Content Security Policy (CSP) headers to reduce CSRF attack surface.

Why prioritize this

This vulnerability warrants immediate prioritization. The CVSS 8.1 rating reflects high impact (complete file deletion capability) with low complexity and network accessibility. Although it requires user interaction (an administrator visiting a malicious page), the attack surface is broad in organizations where administrators browse untrusted content or receive phishing emails. The ability to delete wp-config.php alone represents a business-critical threat: it renders WordPress non-functional and may prevent recovery without backup restoration. Early patch deployment will minimize window of exposure.

Risk score, explained

CVSS 3.1 score of 8.1 (HIGH) is justified: Attack Vector Network and Attack Complexity Low mean the vulnerability is remotely exploitable with no special conditions. Privileges Required None (from the attacker's perspective) reflects that CSRF requires no attacker account. User Interaction Required is the only mitigating factor—but is not a sufficient control when administrators are targeted via social engineering. Integrity Impact High and Availability Impact High reflect that arbitrary file deletion can corrupt website data and shut down services. Confidentiality is unaffected (file contents are not leaked, only deleted). The rating appropriately reflects that this is a severe, easy-to-exploit chain of weaknesses.

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