CVE-2026-16540

Unauthenticated Insecure Direct Object References (IDOR) vulnerability in Simply Schedule Appointments up to version 1.6.12.31.

Simply Schedule Appointments plugin version 1.6.12.29 and earlier contains a Broken Access Control vulnerability that can be exploited without authentication, allowing unauthorized access to functionality.

The Simply Schedule Appointments plugin for WordPress is vulnerable to Local File Inclusion in all versions up to, and including, 1.6.12.27 via the 'ssa_locale' parameter. This makes it possible for authenticated attackers, with subscriber-level access and above, to include and execute arbitrary .php files on the server, allowing the execution of any PHP code in those files. This can be used to bypass access controls, obtain sensitive data, or achieve code execution in cases where .php file types can be uploaded and included. Notably, exploitation does not require authentication in practice, as the locale filter is installed unconditionally on every request during plugins_loaded and the callback performs no nonce or capability check before returning the raw GET parameter value.

Unauthenticated SQL Injection vulnerability in Simply Schedule Appointments versions up to 1.6.12.10.

There is an unauthenticated SQL injection vulnerability in Simply Schedule Appointments versions up to 1.6.9.27.

The Simply Schedule Appointments plugin (up to version 1.6.12.35) is vulnerable to stored XSS due to improper neutralization of input during web page generation. An attacker can inject a malicious script that gets stored and executed.

The Simply Schedule Appointments plugin for WordPress (versions up to and including 1.6.12.35) is vulnerable to stored Cross-Site Scripting via the 'status' parameter due to insufficient input sanitization and output escaping. An unauthenticated attacker can inject arbitrary web scripts into pages that execute when a user accesses the injected page.

The Simply Schedule Appointments plugin by NSquared contains an Authorization Bypass Through User-Controlled Key vulnerability that allows exploiting incorrectly configured access control security levels. This issue affects Simply Schedule Appointments from n/a through 1.6.12.35.

The Simply Schedule Appointments plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 1.6.12.32 via the 'recursive' parameter. Unauthenticated attackers can extract customer PII (names, email addresses, phone numbers, custom form field data) and per-appointment public_token values, which also enables deletion of arbitrary appointments via the DELETE /wp-json/ssa/v1/appointments/{id} endpoint.

The Simply Schedule Appointments plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to and including 1.6.12.31 via the 'complete_group' parameter due to missing validation on a user-controlled key. This allows authenticated attackers with subscriber-level access and above to disclose every co-booker's private id_token and PII, then use each leaked token to read, overwrite arbitrary appointment meta, or cancel the co-booker's appointment.