Ultimate Multisite - Security Vulnerability (CVE-2026-75957)
CVE-2026-75957
The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.15.0 via the `checkout_form` parameter of the `login_customer_after_checkout` function. This is due to the publicly accessible `wu_ajax_nopriv_wu_validate_form` AJAX handler accepting a freely obtainable checkout nonce, and the `checkout_form=wu-finish-checkout` parameter causing `get_validation_rules()` to discard all validation rules while `finish_checkout_form_fields()` returns an empty step list — forcing `is_last_step()` to return true and routing the request directly into full order processing — after which `maybe_create_customer()` resolves the attacker-supplied `email_address` to an existing WordPress user ID without any authentication or ownership verification, and `login_customer_after_checkout()` calls `wp_set_auth_cookie()` for that user ID via a passwordless code path. This makes it possible for unauthenticated attackers to log in as any existing WordPress user — including a Network Super Admin — simply by knowing their email address. Exploitation requires that the targeted user account has no pre-existing Ultimate Multisite customer record; accounts such as a Network Super Admin on a fresh Multisite install, or any administrator or editor added before Ultimate Multisite was configured, satisfy this condition and are therefore exploitable.
CVE-2026-75957
CRITICAL
CVSS 9.8
Published 2026-10-01
Updated 2026-10-01
AI Risk Critical (96/100)
Active Exploit: No strong signal
Published Exploit: No public exploit references
Priority: P1 Immediate
Severity Band
CRITICAL
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected Components
1
Reference Links
10
AI Risk Engine
Critical (96/100)
Exploitability
High
Active Exploitation
No strong signal
Published Exploit Status
No public exploit references
AI Context
Machine-generated threat intelligence
AI
Updated just now
AI enriched just now (2026-10-01 19:55 UTC)
Technical Summary
The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.15.0 via the `checkout_form` parameter of the `login_customer_after_checkout` function. This is due to the publicly accessible `wu_ajax_nopriv_wu_validate_form` AJAX handler accepting a freely obtainable checkout nonce, and the `checkout_form=wu-finish-checkout` parameter causing `get_validation_rules()` to discard all validation rules while `finish_checkout_form_fields()` returns an empty step list — forcing `is_last_step()` to return true and routing the request directly into…
Potential Impact
Severity is CRITICAL (CVSS 9.8). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.
Exploitability Assessment
Exploitability is assessed as High based on low-bar exploit prerequisites.
Primary risk drivers: low-bar exploit prerequisites
Mitigation Recommendations
Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.
Detection & Monitoring
Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.
Business Impact Lens
AI risk score 96/100 (Critical, High) with priority P1 Immediate. Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.
