Executive brief
The Newsletters WordPress plugin uses an insufficiently random method to generate API keys for its optional REST API endpoint, deriving them from the site hostname instead of cryptographic randomness. An attacker who discovers or assumes a target's domain name can compute the valid API key offline and then add/remove email subscribers, send newsletters, and perform other privileged actions without authentication.
Technical details
The vulnerability is a weak cryptographic key generation issue (CWE-326) in the Newsletters plugin's API authentication mechanism. The API key is computed as the MD5 hash of the site hostname, converted to uppercase—a deterministic and publicly knowable input. When the optional API is enabled (not the default), an unauthenticated attacker can derive a valid key using only the target domain name and execute POST requests to /wp-admin/admin-ajax.php?action=newsletters_api with methods like subscriber_add, subscriber_delete, and email/newsletter sending. No user interaction or prior authentication is required. The vulnerability was patched in version 4.17.
Affected products
- Newsletters Newsletters before 4.17
Timeline
- 2026-08-27: disclosed
- 2026-08-29: patched: version 4.17