# Restrict Usernames Emails Characters Plugin <= 5.0.3 - Unauthenticated Missing Authorization to Site-Wide Maintenance Mode (DoS) and Nicename Data Deletion via Bulk Nicename Update Actions

- **ID:** WPSEC-2026-0985
- **Plugin:** Restrict Usernames Emails Characters (`restrict-usernames-emails-characters`), https://wordpress.org/plugins/restrict-usernames-emails-characters/
- **Affected versions:** all versions before 5.1
- **Fixed in:** 5.1 (Update to 5.1 or later.)
- **Severity:** High 8.2 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H)
- **Weakness:** CWE-862
- **Usage among sites WPSec scans:** plugin Low, affected versions None seen (as of 2026-10-15)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/restrict-usernames-emails-characters
- **Fix released:** 2026-10-13
- **Published:** 2026-10-15
- **URL:** https://wpsec.com/vuln/WPSEC-2026-0985/

## Description

The Restrict Usernames Emails Characters plugin for WordPress is vulnerable to unauthorized modification and loss of data via the bulk user_nicename update and process-removal actions in all versions up to, and including, 5.0.3, due to missing capability checks and nonce verification in the val() function (hooked to admin_init) and the wp__loaded() function (hooked to wp_loaded). This makes it possible for unauthenticated attackers to put the whole site into the plugin's maintenance mode, which returns a 503 error to every visitor and administrator for about ten minutes and can be repeated, to empty the plugin's custom author-slug (nicename) table, and to delete the stored state of a running nicename update process.

## References

- https://wpsec.com/vuln/WPSEC-2026-0985/
- https://plugins.svn.wordpress.org/restrict-usernames-emails-characters/tags/5.1/
- https://wordpress.org/plugins/restrict-usernames-emails-characters/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-0985/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Free to use, share and adapt, also commercially, if you credit WPSec and link to this advisory.