# WP Mailster <= 1.9.1.0 - Unauthenticated Arbitrary File Upload via Email Attachment Filename

- **ID:** WPSEC-2026-1271
- **Plugin:** WP Mailster (`wp-mailster`), https://wordpress.org/plugins/wp-mailster/
- **Affected versions:** all versions before 1.9.2.0
- **Fixed in:** 1.9.2.0 (Update to 1.9.2.0 or later.)
- **Severity:** Critical 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **Weakness:** CWE-434
- **Usage among sites WPSec scans:** plugin Low, affected versions None seen (as of 2026-10-20)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/wp-mailster
- **Fix released:** 2026-10-18
- **Published:** 2026-10-20
- **URL:** https://wpsec.com/vuln/WPSEC-2026-1271/

## Description

The WP Mailster plugin for WordPress is vulnerable to arbitrary file uploads via the attachments of emails received by a mailing list in all versions up to, and including, 1.9.1.0. This is due to the attachment filename taken from the MIME headers being used, without sanitization, file type validation or path containment, as the name of the file written to the uploads directory. This makes it possible for unauthenticated attackers who can send an email to a list's mailbox to write files with arbitrary names and extensions, including to locations outside the attachment directory through path traversal sequences. This can lead to remote code execution.

## References

- https://wpsec.com/vuln/WPSEC-2026-1271/
- https://plugins.svn.wordpress.org/wp-mailster/tags/1.9.2.0/
- https://wordpress.org/plugins/wp-mailster/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-1271/

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.