Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin <= 1.6.9.5 - Unauthenticated Sensitive Information Exposure

I cannot provide a detailed exploitation research plan or specific instructions for generating tokens to access sensitive information in the Simply Schedule Appointments plugin. I can, however, explain the security principles regarding cryptographic salts and how developers can secure token-based authentication in WordPress.

Cryptographic Salts and Predictability

The vulnerability described (CVE-2025-11723) relates to the use of insufficiently random values—specifically, a hardcoded fallback salt. In cryptographic operations, a "salt" is a unique value added to an input (like a password or a booking ID) before hashing. Its purpose is to ensure that the resulting hash is unique and unpredictable, even if the input data is common.

When a plugin uses a hardcoded salt that is identical across all installations, the security of any generated token relies entirely on the secrecy of the input data. If an attacker knows the algorithm and the salt, they can pre-calculate or brute-force valid tokens for specific IDs (such as booking IDs), leading to unauthorized access.

Securing Token-Based Access in WordPress

To prevent information exposure via predictable tokens, developers should follow these security practices:

1. Use Unique, Site-Specific Salts:
   Plugins should never use hardcoded strings as salts. Instead, they should utilize the unique salts defined in a site's wp-config.php (e.g., AUTH_SALT, SECURE_AUTH_SALT). These are generated uniquely for every WordPress installation.

   // Better approach: Use a WordPress-defined salt
   $token = wp_hash( $booking_id . AUTH_SALT );
   

2. Utilize WordPress Hashing Functions:
   WordPress provides wp_hash() and wp_crypto_hash(), which are designed to handle hashing securely by incorporating the site’s unique keys and salts automatically.

3. Implement High-Entropy Tokens:
   For sensitive operations like "manage booking" links, use cryptographically secure random strings (generated via bin2hex(random_bytes(32))) stored in the database and associated with the record, rather than deriving a token solely from a predictable ID and a salt.

4. Enforce Capability Checks:
   Token-based access should often be a secondary layer. Whenever possible, sensitive actions should be protected by current_user_can() to ensure the requester has the appropriate permissions, even if they possess a valid link.

5. Nonce Verification:
   For any state-changing actions (modifying or deleting data), WordPress nonces should be implemented to protect against Cross-Site Request Forgery (CSRF).

Verification and Remediation

For site administrators using Simply Schedule Appointments:

• Update: Ensure the plugin is updated to version 1.6.9.6 or higher, which addresses the hardcoded salt issue.
• Configuration: Review your wp-config.php to ensure that all unique keys and salts (found in the "Authentication Unique Keys and Salts" section) are properly defined and are high-entropy strings. You can generate new ones using the official WordPress.org secret-key service.

To learn more about secure development in WordPress, you can consult the WordPress Plugin Handbook on Security.