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CVE-2026-78159 – Unauthenticated Remote Code Execution – The Events Calendar (WordPress Plugin) ≤ 6.

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Summary

CVE-2026-78159 is a critical unauthenticated Remote Code Execution vulnerability in The Events Calendar, a WordPress plugin developed by StellarWP. The flaw stems from insufficient validation of widget "classes" data, allowing an attacker-supplied plain-array payload to bypass a safety check and reach a callable-invocation code path. It affects all versions of the plugin through 6.17.3 and carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: Insufficient validation in the widget classes map allows a plain-array payload to bypass the plugin’s is_safe_widget_instance() object check, reaching the callable-invocation sink inside Element_Classes::parse_array().
  • Trigger conditions: The target site must have comments enabled on tribe_events posts, and a comment containing a crafted wp:legacy-widget block must exist. The vulnerable code path is triggered when do_blocks() processes the single-event page HTML, including the comment area.
  • Attack vector: Network-based and unauthenticated — no login, privileges, or user interaction are required (AV:N/AC:L/PR:N/UI:N).
  • Impact: Full compromise of confidentiality, integrity, and availability, as the flaw allows arbitrary code execution on the affected server.
  • Weakness classification: CWE-94, Improper Control of Generation of Code ("Code Injection").

Affected software

  • The Events Calendar (WordPress plugin) by StellarWP — all versions through 6.17.3.

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade The Events Calendar plugin to version 6.17.4 or later, which corrects the validation logic in parse_array() and strengthens the checks performed by is_safe_widget_instance().
  • If immediate patching is not possible:
    • Disable comments on tribe_events posts (via WordPress discussion settings or a custom filter) to remove the trigger path for the attack.
    • Audit existing comment content for any previously injected wp:legacy-widget blocks and remove them.
    • Consider a Web Application Firewall rule to block malformed serialized/array payloads submitted through comment fields.
  • Note: A related follow-on issue (tracked separately as CVE-2026-78006) affecting the same is_safe_widget_instance() bypass logic was identified in versions up to and including 6.17.4; sites should apply the latest available plugin release beyond 6.17.4 to ensure full protection.

References

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