CVE-2026-87111 WPEverest CVE debrief

Who should care

Defenders responsible for WordPress installations with the User Registration PRO plugin, particularly those using premium build versions up to 6.2.9, should assess exposure and verify the effectiveness of current input sanitization and output escaping measures.

Why it matters

The User Registration PRO plugin for WordPress is vulnerable to Stored Cross-Site Scripting via HTTP Referer Header, allowing unauthenticated attackers to inject arbitrary web scripts. Defenders should prioritize verifying exposure and assessing the effectiveness of current input sanitization and output escaping measures.

• Unauthenticated attackers can inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
• The vulnerability is present only in the premium build of the plugin and is not present in the free WordPress.org distribution.
• The nonce required to call the vulnerable AJAX endpoint is localized into the page source of every front-end page for anonymous visitors, making it fully obtainable by unauthenticated attackers.
• Defenders should verify exposure of premium build versions up to 6.2.9 and assess the effectiveness of current input sanitization and output escaping measures.

Technical summary

The User Registration PRO – Custom Registration Form, Login Form, and User Profile WordPress Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via HTTP Referer Header in all versions up to, and including, 6.2.9 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

Defensive priority

Defenders should prioritize verifying exposure of premium build versions up to 6.2.9 and assess the effectiveness of current input sanitization and output escaping measures.

Recommended defensive actions

• Verify exposure of premium build versions up to 6.2.9
• Assess effectiveness of current input sanitization and output escaping measures
• Implement compensating controls to restrict access to vulnerable AJAX endpoint
• Review relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

The vulnerability is present only in the premium build of the plugin and is not present in the free WordPress.org distribution. The nonce required to call the vulnerable AJAX endpoint is localized into the page source of every front-end page for anonymous visitors, making it fully obtainable by unauthenticated attackers.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.