# ActivityPub <= 9.4.0 - Unauthenticated Comment Moderation Bypass via Identity Spoofing

- **ID:** WPSEC-2026-2578
- **Plugin:** ActivityPub (`activitypub`), https://wordpress.org/plugins/activitypub/
- **Affected versions:** from 4.1.0 before 9.4.1
- **Fixed in:** 9.4.1 (Update to 9.4.1 or later.)
- **Severity:** Medium 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **Weakness:** CWE-290
- **Usage among sites WPSec scans:** plugin Low, affected versions Low (as of 2026-11-05)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/activitypub
- **Fix released:** 2026-11-04
- **Published:** 2026-11-05
- **URL:** https://wpsec.com/vuln/WPSEC-2026-2578/

## Description

The ActivityPub plugin for WordPress is vulnerable to comment moderation bypass via identity spoofing in all versions up to, and including, 9.4.0, due to the plugin's previous-approval check for Fediverse replies matching only the author name and author URL, both taken from the remote actor's profile, and later also storing an author email built from the actor-supplied 'url' field without checking it against the signed actor. Comments typed into the comment form with a Fediverse name and handle were also matched against Fediverse comment history. This makes it possible for unauthenticated attackers, on sites using the 'Comment author must have a previously approved comment' setting (the WordPress default), to impersonate a previously approved commenter and have their comments approved automatically, bypassing moderation.

## References

- https://wpsec.com/vuln/WPSEC-2026-2578/
- https://plugins.svn.wordpress.org/activitypub/tags/9.4.1/
- https://wordpress.org/plugins/activitypub/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-2578/

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.