OTP Login & Register Woocommerce <= 2.7.2 - Unauthenticated Authentication Bypass via Brute Force

The OTP Login & Register Woocommerce plugin for WordPress is vulnerable to Authentication Bypass via OTP Brute Force in all versions up to, and including, 2.7.2. The vulnerability exists because the OTP rate-limit attempt counter in `process_otp_form` is keyed exclusively on the attacker-controlled `xoo_ml_user_ip_data` cookie's `ip_address` field, allowing unlimited counter resets by simply rotating the cookie, while the OTP itself is generated with PHP's non-cryptographic `rand()` function over a default space of only 9,000 possible values (1000–9999), and both the OTP issuance endpoint (`xoo_ml_login_with_otp`) and verification endpoint (`xoo_ml_otp_form_submit`) are registered as unauthenticated `wp_ajax_nopriv` actions with no nonce or capability checks. This makes it possible for unauthenticated attackers to brute-force the OTP for any registered account and obtain a full WordPress authentication session — including for administrator accounts — via `wp_set_auth_cookie()` in `login_user_with_otp()`. Exploitation requires the attacker to know the target user's registered phone number, which is used to trigger OTP issuance via the unauthenticated `xoo_ml_login_with_otp` endpoint.

Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: OTP Login & Register Woocommerce 2.7.3 closes this, and updating the plugin is the step that ends it.

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