# CVE-2026-75957: Ultimate Multisite <= 2.15.0 - Unauthenticated Authentication Bypass via 'checkout_form' Parameter

> Unauthenticated attackers can log in as any existing WordPress user, including admins, by supplying their email address to a vulnerable AJAX handler.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Oct 2026
- **Updated:** 1 Oct 2026
- **Also known as:** GHSA-xr7j-wm8w-c5p4

## What is CVE-2026-75957?

CVE-2026-75957 is a critical authentication bypass vulnerability in superdav42 Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform, published on 1 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-75957?


## How do I fix CVE-2026-75957?

No fix has been published for CVE-2026-75957 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-75957 being exploited?

There is no known exploitation of CVE-2026-75957 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-75957 and fix it if it is affected.

What it is: CVE-2026-75957 is a critical authentication bypass vulnerability in superdav42 Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform, published on 1 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-75957 in the wild and no public exploit code.

Affected product: superdav42 Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-75957/ (Markdown: https://insights.sbomify.com/CVE-2026-75957/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-75957
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75957
- OSV: https://osv.dev/vulnerability/CVE-2026-75957

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-75957/
Summaries are generated and may contain mistakes; the official description above is the record.