User Session Synchronizer <= 1.4.0 — Unauthenticated Authentication Bypass to Account Takeover via 'ussync-key', 'ussync-token', and 'ussync-ref' Parameters

Am I affected?

• Check your version: in wp-admin go to Plugins → Installed Plugins and read the version under User Session Synchronizer.
• No admin access? Run a passive check of your site. It reads public files only.
• No account is needed to exploit this. Treat any exposed site on an affected version as at risk.

What to do

1. No known patch available. Please review the vulnerability's details in depth and employ mitigations based on your organization's risk tolerance. It may be best to uninstall the affected software and find a replacement.
2. Rotate administrator passwords and application secrets if the site ran a vulnerable version while publicly reachable.
3. Watch User Session Synchronizer to get an email when the next vulnerability is published.

Advisory

Source description from Wordfence Intelligence, credited to Afan, moonge.

The User Session Synchronizer plugin for WordPress is vulnerable to Authentication Bypass leading to Account Takeover in all versions up to, and including, 1.4.0. The `synchronize_session()` function, hooked on `init` and therefore executed on every request, performs no nonce, capability, or shared-secret validation against the attacker-supplied `ussync-key`, `ussync-token`, and `ussync-ref` parameters; when `ussync-key` references an unregistered slot, `get_option()` returns `false` for both the secret key and the domain list, causing the AES-256-CBC encryption key to degrade to the fully predictable `md5('')` and the referer allowlist to collapse to an empty-string match, while the AES IV is unconditionally hard-coded as `md5('another-secret')`. This makes it possible for unauthenticated attackers to supply a crafted request encrypting any known or guessable user email address in the `ussync-ref` parameter, causing the handler to call `wp_set_auth_cookie()` for the matched user and granting full authentication as that user — including administrators — with no prior knowledge of site secrets.

Exploits & references

Proof-of-concept & detection

No public proof-of-concept or detection template is known for this vulnerability.

Advisories & patches

• Advisorywordfence.com

Related CVEs

Timeline

1. Aug 14, 2026

   CVE published

   Severity critical, CVSS 9.8

2. Nov 13, 2026

   Record last updated