The Events Calendar <= 6.17.4 - Unauthenticated PHP Object Injection to Remote Code Execution

Summary

The The Events Calendar plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 6.17.4 via the is_safe_widget_instance function. This is due to insufficient protection in is_safe_widget_instance, which can be bypassed because PHP fires magic methods during its pre-parse, combined with enable_rendering_widget_copied() forging a valid wp_hash integrity attribute before unserialize() is reached. This makes it possible for unauthenticated attackers to execute code on the server. This is exploitable without authentication or approval because the plugin's V2 single-event template runs do_blocks() over buffered comment HTML, and WordPress returns a moderation-hash URL that allows an unauthenticated commenter to immediately view their own pending comment, delivering the injected block markup to the vulnerable code path before any moderation occurs. This does require comments to be enabled and visible on events.

Timeline

1. Sep 12, 2026, 7:39 AM UTCCVE published
2. Sep 14, 2026, 7:08 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: total

3. Sep 14, 2026, 7:23 PM UTCRecord last updated

Affected versions

• stellarwp The Events Calendar

  through 6.17.4

References 9