# Meta Box - WordPress Custom Fields Framework <= 5.15.2 - Authenticated (Contributor+) Stored Cross-Site Scripting via Background Field

- **ID:** WPSEC-2026-1299
- **Plugin:** Meta Box – A Framework for Dynamic Websites (`meta-box`), https://wordpress.org/plugins/meta-box/
- **Affected versions:** all versions before 5.15.3
- **Fixed in:** 5.15.3 (Update to 5.15.3 or later.)
- **Severity:** Medium 6.4 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N)
- **Weakness:** CWE-79
- **Usage among sites WPSec scans:** plugin Low, affected versions Low (as of 2026-10-21)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/meta-box
- **Fix released:** 2026-10-20
- **Published:** 2026-10-21
- **URL:** https://wpsec.com/vuln/WPSEC-2026-1299/

## Description

The Meta Box plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the background field in all versions up to, and including, 5.15.2 due to the sanitizer preserving arbitrary submitted array keys and the formatter concatenating those keys into the output without escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts that execute whenever a user accesses a page where the background field value is rendered. Exploitation requires a background field to be registered on content the attacker can edit.

## References

- https://wpsec.com/vuln/WPSEC-2026-1299/
- https://plugins.svn.wordpress.org/meta-box/tags/5.15.3/
- https://wordpress.org/plugins/meta-box/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-1299/

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.