CVE-2026-15826 PoC — User Profile Builder <= 3.16.4 - Unauthenticated Authentication Bypass via Type Confusion to Administrator Account Takeo

Source

https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-15826.yaml

Associated Vulnerability

Title: User Profile Builder <= 3.16.4 - Unauthenticated Authentication Bypass via Type Confusion to Administrator Account Takeover via 'username' Parameter (CVE-2026-15826)
Description:The User Profile Builder plugin for WordPress is vulnerable to Authentication Bypass via Type Confusion in versions up to, and including, 3.16.4. This is due to the wppb_log_in_user() function calling absint() on the return value of wp_insert_user() before performing an is_wp_error() check — when a registration is submitted with a 61–70 character username, WordPress core rejects it with a WP_Error object, but absint() coerces that object to the integer 1 before the error check can short-circuit execution, causing the plugin to bind and return a transient-backed autologin nonce tied to user ID 1. This makes it possible for unauthenticated attackers to log in as the site's Administrator account (user ID 1), resulting in full administrative takeover of the site.

Description

The User Profile Builder plugin for WordPress version 3.16.4 is vulnerable to an authentication bypass via type confusion. Profile Builder's automatic-login-after-registration handler passes the return value of wp_insert_user() through absint() before testing it with is_wp_error(), so the error check runs against the already-coerced integer. A registration submitted with a 61-70 character username passes the plugin's own validation but is rejected by WordPress core, because the user_login column is VARCHAR(60), and wp_insert_user() returns a WP_Error object. absint() coerces that object to the integer 1, is_wp_error(1) is false, and the plugin binds a transient-backed autologin nonce to user ID 1. Consuming that nonce calls wp_set_auth_cookie(1) and logs the unauthenticated attacker in as the site's Administrator.

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