The vulnerability identified as CVE-2025-12787 affects the Hydra Booking — Appointment Scheduling & Booking Calendar plugin for WordPress, versions up to and including 1.1.27. The root cause is the plugin's "tfhb_meeting_form_submit_callback" function generating booking cancellation tokens using insufficiently random values combined with a globally shared nonce. This weak token generation allows unauthenticated attackers to perform brute force attacks against the tfhb_meeting_form_cencel AJAX endpoint to cancel arbitrary bookings without authorization. The vulnerability is classified under CWE-330, which concerns the use of insufficiently random values leading to predictable security tokens. The CVSS v3.1 base score is 5.3 (medium severity), reflecting that the attack vector is network-based (AV:N), requires no privileges (PR:N), no user interaction (UI:N), and impacts integrity (I:L) but not confidentiality or availability. No patches or known exploits are currently available, indicating that the vulnerability is newly disclosed. The attack could disrupt business operations by allowing malicious actors to cancel legitimate appointments, potentially causing reputational damage and operational inefficiencies for organizations relying on this plugin for scheduling.

For European organizations, this vulnerability poses a risk primarily to the integrity of appointment and booking data. Unauthorized cancellation of bookings can lead to operational disruptions, loss of customer trust, and potential financial impacts due to missed appointments or service delivery failures. Organizations in sectors such as healthcare, professional services, and retail that rely heavily on online appointment scheduling are particularly vulnerable. While the vulnerability does not expose sensitive personal data or cause denial of service, the ability to manipulate bookings without authentication can be exploited for targeted disruption or harassment. The impact is amplified in environments where the plugin is widely used and integrated into critical customer-facing workflows. Additionally, the lack of authentication and user interaction requirements lowers the barrier for attackers, increasing the likelihood of exploitation if unpatched.

Since no official patch is currently available, European organizations should implement immediate compensating controls. These include deploying web application firewalls (WAFs) with rules to detect and block brute force attempts against the tfhb_meeting_form_cencel AJAX endpoint. Rate limiting requests to this endpoint can reduce the feasibility of brute force token guessing. Organizations should monitor logs for unusual cancellation patterns and implement alerting for suspicious activity. Where possible, temporarily disabling the booking cancellation feature or restricting it to authenticated users can mitigate risk. Once a vendor patch is released, prompt application of the update is critical. Additionally, organizations should review token generation mechanisms in their plugins and consider contributing to or requesting improvements in randomness and nonce management from the vendor. Regular security assessments of WordPress plugins and adherence to the principle of least privilege for plugin permissions are recommended.