CVE-2016-20069: Unauthenticated SQL Injection in WordPress Booking Calendar Contact Form 1.0.23

Technical summary

CVE-2016-20069 is a blind SQL injection vulnerability (CWE-89) in the WordPress Booking Calendar Contact Form plugin (version 1.0.23). The vulnerable code exists in a shortcode handler that accepts a 'calendar' parameter and uses it directly in database queries without sanitization or parameterized query protection. This is a network-accessible, unauthenticated vulnerability requiring no user interaction or special conditions—attackers can craft malicious shortcode invocations via published pages or posts containing the vulnerable shortcode, injecting SQL payloads that extract data from wp_users, wp_usermeta, wp_options, and other sensitive tables. The blind nature means attackers must use time-based or boolean-based inference techniques to extract data, but exploitation is straightforward.

Business impact

A successful exploitation could expose sensitive customer information, user credentials, email addresses, and database configuration details. For WordPress sites using this plugin, attackers gain a direct path to extract private customer data, potentially leading to regulatory compliance violations (GDPR, CCPA), reputational damage, and credential compromise that facilitates lateral attacks. The plugin's contact form functionality suggests it may collect client inquiries, making data theft particularly damaging for business relationships.

Affected systems

WordPress installations with Booking Calendar Contact Form plugin version 1.0.23 are vulnerable. The vendor product list is unavailable in structured data; verify your deployment against the plugin repository to confirm installed versions. Any WordPress site publicly displaying pages or posts using the vulnerable shortcode is at risk.

Exploitability

This vulnerability is highly exploitable. No authentication is required, and attackers need only issue standard HTTP requests to a WordPress page or post containing the vulnerable shortcode with injected SQL in the calendar parameter. Blind SQL injection techniques using time delays or conditional logic allow data extraction without direct error feedback. Exploit development requires moderate skill but has been documented in public disclosures; automated scanning tools can identify vulnerable installations by probing shortcode endpoints.

Remediation

Upgrade to a patched version of Booking Calendar Contact Form released after version 1.0.23—verify the exact patch version against the plugin's official repository or vendor advisory. If no patch is available, disable or remove the plugin entirely until a fix is released. As an interim compensating control, use Web Application Firewall (WAF) rules to block requests with SQL syntax in the calendar parameter.

Patch guidance

Check the Booking Calendar Contact Form plugin page on wordpress.org for available updates. Review the vendor advisory or changelog to confirm which version addresses CVE-2016-20069. Apply the update through the WordPress admin dashboard once verified. If the plugin developer has not released a patch and none is anticipated, consider migrating to an alternative booking or contact form plugin with active maintenance and security focus. Test any upgrade in a staging environment first.

Detection guidance

Monitor web server logs for requests containing the booking calendar shortcode with SQL keywords (e.g., 'SELECT', 'UNION', 'ORDER BY') in the calendar parameter. Enable WordPress security plugins with SQL injection detection capabilities. Check database query logs for unusual SQL patterns or excessively long queries originating from the shortcode handler. Review database user privilege logs for unauthorized data exports or access to sensitive tables. A WAF with SQL injection signatures can flag exploit attempts before they reach WordPress.

Why prioritize this

This vulnerability merits immediate patching priority due to its high CVSS score (8.2), public accessibility without authentication, minimal attack complexity, and direct exposure of confidential data. The blind SQL injection nature may delay detection, allowing attackers prolonged database access. For any organization with active Booking Calendar Contact Form deployments, this is a critical remediation item.

Risk score, explained

CVSS 3.1 score of 8.2 (HIGH) reflects: network-accessible attack vector, low complexity, no authentication required, no user interaction needed, and high confidentiality impact (full database read access). The scope is unchanged and integrity impact is low because SQL injection here primarily enables data exfiltration rather than modification, though attackers may craft queries to update records. The absence of availability impact (denial-of-service) slightly reduces the score from maximum severity.

Frequently asked questions