Executive Summary

The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress has a vulnerability that allows denial of service attacks. This happens because a publicly accessible REST API endpoint (/wp-json/ssa/v1/async) uses PHP's sleep() function with a user-supplied delay parameter without any rate limiting.

An attacker can exploit this by sending many requests that cause PHP processes to sleep, which exhausts the available PHP worker processes and prevents legitimate users from accessing the site.

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Compliance Impact

This vulnerability causes a denial of service by exhausting PHP worker processes through an unauthenticated REST API endpoint. It does not directly impact the confidentiality or integrity of data.

Since the vulnerability does not involve unauthorized access to personal or sensitive data, it does not directly affect compliance with standards like GDPR or HIPAA, which focus on data protection and privacy.

However, denial of service could indirectly affect availability requirements under these regulations, potentially impacting service continuity obligations.

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Impact Analysis

This vulnerability can impact you by causing a denial of service on your WordPress site using the affected plugin. An attacker can make the site unresponsive by exhausting PHP worker processes, which means legitimate users will be unable to access the site or use its appointment booking features.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual or excessive requests to the REST API endpoint /wp-json/ssa/v1/async on your WordPress site.

Specifically, you can look for repeated unauthenticated requests that include a delay parameter causing PHP's sleep() function to be invoked.

Commands to detect this might include using web server logs or network monitoring tools to filter requests to the vulnerable endpoint.

• Using grep on access logs: grep "/wp-json/ssa/v1/async" /var/log/apache2/access.log
• Using curl to test the endpoint: curl -v "https://yourdomain.com/wp-json/ssa/v1/async?delay=10"
• Monitoring PHP worker usage to detect exhaustion, e.g., using top or ps commands.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable REST API endpoint to prevent unauthenticated requests.

You can implement rate limiting on the /wp-json/ssa/v1/async endpoint to prevent abuse of the sleep() function.

Alternatively, temporarily disabling or blocking access to the endpoint via web server configuration or firewall rules can reduce the risk.

Updating the Appointment Booking Calendar plugin to a version later than 1.6.11.5, once available, is recommended for a permanent fix.

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