CVE-2026-66451

Executive Summary

CVE-2026-66451 is an unauthenticated broken authentication vulnerability affecting the WP Event Solution WordPress plugin, version 4.1.9 and earlier. The flaw allows a remote, unauthenticated attacker to bypass authentication mechanisms, potentially leading to unauthorized access to application functions, low-impact data disclosure, and unauthorized modification of affected data. With a CVSS score of 6.5 (Medium severity), the vulnerability is network-exploitable without requiring user interaction or elevated privileges, making it a viable target for broad opportunistic scanning of WordPress installations.

Technical Analysis

The vulnerability is classified under CWE-288 (Authentication Bypass Using an Alternate Path). The NVD description states the flaw exists in the WP Event Solution plugin, version 4.1.9 and earlier, and is characterized as "Unauthenticated Broken Authentication." This classification indicates that the plugin's authentication logic contains a flaw that permits attackers to bypass normal authentication checks without providing valid credentials.

The vulnerability resides in the plugin's authentication mechanism. The CVSS vector (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N) provides the following technical details:

• Attack Vector: Network (AV:N) — the vulnerability is exploitable remotely over the network
• Attack Complexity: Low (AC:L) — no special conditions or race conditions required for exploitation
• Privileges Required: None (PR:N) — the attacker does not need any prior authentication or authorization
• User Interaction: None (UI:N) — no victim interaction is required to trigger the flaw
• Scope: Unchanged (S:U) — exploitation does not affect resources beyond the vulnerable component
• Confidentiality Impact: Low (C:L) — limited information disclosure possible
• Integrity Impact: Low (I:L) — limited unauthorized modification of data possible
• Availability Impact: None (A:N) — the vulnerability does not affect system availability

The attack surface is the web-facing WordPress installation running the WP Event Solution plugin. Since WordPress plugins execute in the context of the web server and the WordPress application, a successful authentication bypass could allow an attacker to invoke protected functions or administrative operations within the plugin's scope. The plugin, being an event management solution, likely exposes various user-facing and administrative endpoints through WordPress's admin-ajax.php, admin-post.php, or REST API routes — any of which may be affected by the broken authentication logic.

The root cause is likely a failure to properly validate authentication tokens, cookies, or nonce values in one or more plugin functions. Without valid session validation, the plugin may incorrectly assume a request is authenticated, permitting unauthorized access to plugin functionality that should require a logged-in user or administrative privileges.

Exploitation Scenarios

The following attack chain describes how an attacker would exploit CVE-2026-66451:

1. Reconnaissance and Target Identification: The attacker uses search engines or scanning tools (e.g., Shodan, Censys, or internet-wide scanning with tools like Masscan) to identify WordPress sites running the WP Event Solution plugin. The attacker can fingerprint the plugin by requesting common plugin assets, such as wp-content/plugins/event-solution/readme.txt (if it exists) or by inspecting page source for plugin-specific CSS/JS file paths that reveal the plugin directory name. Alternatively, WordPress site enumeration through the REST API (/wp-json/wp/v2/plugins) or plugin version detection via readme.txt can confirm the version is <= 4.1.9.

2. Weaponization and Trigger: The attacker crafts a specially constructed HTTP request to a vulnerable endpoint within the plugin. Since the flaw is a broken authentication issue, the attacker will send requests to plugin-specific administrative or protected action handlers without providing any authentication credentials. The attacker may target:

   • AJAX actions registered by the plugin (e.g., admin-ajax.php?action=event_solution_[protected_action])
   • Admin-post handlers (admin-post.php with plugin-specific actions)
   • Custom REST API endpoints exposed by the plugin The attacker omits any authentication cookies, nonces, or other security tokens that the plugin should require for the action to execute.

3. Payload and Execution: The HTTP request is sent with no authentication headers or cookies. Because the plugin fails to verify the user's authentication status before processing the request, the vulnerable code path executes as if the request came from an authenticated user. The attacker may include parameters to trigger specific plugin functions, such as retrieving event data, creating or modifying event records, or accessing configuration options. The exact parameters depend on the plugin's exposed functions, but a generic example would be:

   POST /wp-admin/admin-ajax.php HTTP/1.1
   Host: victim-site.com
   Content-Type: application/x-www-form-urlencoded
   
   action=event_solution_some_protected_action&event_id=123&field=value
   

   The server processes this request and returns data or executes the action without demanding valid session credentials.

4. Post-Exploitation Impact: Successful exploitation allows the attacker to:

   • Read sensitive event data or configuration (Confidentiality Impact: Low)
   • Modify event records, settings, or other plugin data (Integrity Impact: Low)
   • Potentially chain the vulnerability with other flaws (e.g., stored XSS) if the attacker can inject content into event fields that are rendered to other users
   • Enumerate plugin functionality to identify additional attack vectors within the WordPress installation

If the plugin exposes administrative functions (e.g., settings management), the attacker could modify plugin settings, potentially disabling security features or redirecting users to malicious sites.

Impact Assessment

The CVSS base score of 6.5 (Medium) reflects a moderate risk profile. The vulnerability is remotely exploitable without authentication or user interaction, which significantly expands the potential attacker pool to anyone with network access to the target. However, the low confidentiality and integrity impacts limit the direct damage: the attacker gains limited read/write access to plugin-specific data but not full site compromise.

Business impact is contingent on the data handled by the WP Event Solution plugin. If the plugin manages event registrations, attendee information, or payment-related data, the confidentiality breach could expose personal or financial information. Integrity impacts could result in altered event listings, tampered registration data, or manipulated calendar displays, potentially causing operational disruption or reputational harm for organizations relying on the plugin for public-facing event management.

The blast radius is confined to the plugin's data and functionality — the vulnerability does not inherently lead to remote code execution or full WordPress administrator compromise. However, successful exploitation could serve as a foothold for further attacks, such as:

• Uploading malicious files if the plugin has file-upload functionality exposed through the broken authentication path
• Injecting malicious content that triggers stored XSS when viewed by legitimate administrators
• Accessing nonce values or other secrets that could be used to forge additional authenticated requests

The Medium severity rating appropriately reflects the balance between ease of exploitation (network, no auth) and limited direct impact (Low/Low/None for CIA triad).

Detection Guidance

Sigma Rule

title: WP Event Solution Unauthenticated Authentication Bypass Attempt
id: 7b8e4a2c-3d5f-4a6b-8c9d-1e2f3a4b5c6d
status: experimental
description: Detects unauthenticated requests targeting WP Event Solution plugin protected actions
logsource:
  category: webserver
  product: apache
detection:
  selection:
    cs-uri-query|contains:
      - 'action=event_solution'
      - 'admin-post.php'
      - 'wp-ajax'
    sc-status:
      - '200'
      - '403'
  filter_known_traffic:
    cs-username: 'exists'
  condition: selection and not filter_known_traffic
level: medium
falsepositives:
  - Legitimate unauthenticated requests to public plugin features
  - Plugin's public-facing event submission forms
tags:
  - attack.t1190
  - cve.2026-66451

YARA Rule

rule WP_Event_Solution_Auth_Bypass
{
    meta:
        author = "Valters IT Security"
        description = "Detects HTTP requests attempting to exploit CVE-2026-66451 authentication bypass"
        cve = "CVE-2026-66451"
        date = "2025-05-14"
        severity = "medium"
    strings:
        $a1 = "wp-content/plugins/event-solution" ascii wide
        $a2 = "event_solution_" ascii wide
        $a3 = "admin-ajax.php" ascii wide
        $a4 = "action=event_solution" ascii wide
        $b1 = "UNAUTHENTICATED" ascii wide nocase
    condition:
        (uint16(0) == 0x5A4D or uint16(0) == 0x4D5A or #a1 > 0) and
        any of ($a*) and not any of ($b*)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"CVE-2026-66451 WP Event Solution Authentication Bypass Attempt"; flow:established,to_server; content:"GET"; http_method; content:"/wp-admin/"; http_uri; content:"admin-ajax.php"; http_uri; content:"action=event_solution"; http_uri; nocase; content:"Cookie"; http_header; pcre:"/Cookie:\s*(?!.*wordpress_logged_in)/i"; classtype:attempted-admin; sid:2026664511; rev:1; metadata:created_at 2025_05_14, cve CVE-2026-66451;)

Elastic Detection

sequence by source.ip with maxspan=5m
  [network where destination.port == 80 and
   http.request.body.text contains "action=event_solution"]
  [network where destination.port == 80 and
   not http.request.headers.cookie contains "wordpress_logged_in"]

Splunk SPL Query

index=web sourcetype=access_combined
| where like(uri_path, "%admin-ajax.php%") OR like(uri_path, "%admin-post.php%")
| search uri_query="*event_solution*"
| eval has_auth_cookie = if(match(cookie, "wordpress_logged_in"), "yes", "no")
| search has_auth_cookie="no"
| stats count by src_ip, uri_query, status
| where count > 5
| table _time, src_ip, uri_query, count, status

Wazuh OSSEC Rule

<group name="wordpress,">
  <rule id="931095" level="8">
    <decoded_as>web</decoded_as>
    <match>event_solution_</match>
    <regex>admin-ajax\.php|admin-post\.php</regex>
    <description>WP Event Solution (CVE-2026-66451) unauthenticated action request detected</description>
    <group>authentication_failures,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No patch evidence exists from any tracked source. The vendor has not released a fixed version, and no vendor advisory or patch commit has been identified. The affected version range remains "<= 4.1.9."

1. Immediate Mitigations:

   • Disable the plugin: If WP Event Solution is not essential to business operations, deactivate and remove it immediately to eliminate the attack surface.
   • Restrict network access: Use a Web Application Firewall (WAF) to block requests to the plugin's PHP files, AJAX endpoints, or any URL containing the event-solution path.
   • Monitor and audit: Enable detailed access logging for all WordPress admin and AJAX endpoints. Alert on any unauthenticated requests containing event_solution_ strings.
   • Review current data: Check for signs of unauthorized modifications to event records, settings, or user data that may indicate prior exploitation.

2. Patch/Upgrade Steps:

   • Monitor the WordPress plugin repository and the vendor's official channels for a patched release. Once a version higher than 4.1.9 is available, update the plugin immediately through the WordPress admin dashboard (Plugins → Installed Plugins → Update) or via WP-CLI: wp plugin update event-solution.
   • If the plugin is not listed in the WordPress repository but obtained from a third-party source, verify the authenticity of the update source and confirm the fix addresses CVE-2026-66451.
   • Subscribe to WordPress security mailing lists and the vendor's official announcements for patch release notifications.

3. Long-Term Hardening:

   • Least privilege principle: Ensure the plugin runs with minimal required permissions. Review and restrict the plugin's file permissions to prevent unauthorized modification if the plugin directory is compromised.
   • Regular vulnerability scanning: Implement continuous scanning of WordPress core, themes, and plugins using automated tools (e.g., WPScan, Nessus) to identify vulnerable components early.
   • Backup strategy: Maintain regular backups of the WordPress installation, including the database, to enable rapid recovery in case of data integrity compromise.
   • Hardening WordPress: Implement Wordfence or similar security plugins, disable file editing in wp-config.php (define('DISALLOW_FILE_EDIT', true);), and enforce strong admin passwords and two-factor authentication.
   • Audit plugin usage: Evaluate whether event management functionality is necessary and whether alternative maintained plugins are available.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-66451
2. CWE-288 Authentication Bypass Using an Alternate Path: https://cwe.mitre.org/data/definitions/288.html
3. WordPress Plugin Repository (to monitor for patched versions): https://wordpress.org/plugins/
4. MITRE ATT&CK Technique T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/

Threat Actor Campaigns / Exploit-in-the-Wild: No known active exploitation campaigns or exploits-in-the-wild have been reported for CVE-2026-66451 at the time of writing. The PoC status is Unknown, indicating that no public proof-of-concept code has been identified, though the vulnerability class (authentication bypass in WordPress plugins) is frequently targeted by botnets and opportunistic attackers. The plugin's presence on WordPress sites makes it a candidate for mass scanning campaigns, and administrators should assume the vulnerability is being probed even without confirmed exploit code. CISA has not added this CVE to the Known Exploited Vulnerabilities (KEV) catalog.