Description

The Simple Membership MailChimp Integration WordPress plugin before 1.9.8 does not have CSRF checks in its settings page, allowing attackers to trick a logged-in administrator into changing the configured third-party API key. Once replaced, all subsequent member registration data (name, email, membership level) is sent to the attacker-controlled account.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.4",
  "pubDate": "2026-09-02T15:17:46.090Z",
  "pubdate": "2026-09-02T15:17:46.090Z",
  "executiveSummary": "The Simple Membership MailChimp Integration plugin for WordPress is susceptible to a Cross-Site Request Forgery (CSRF) vulnerability affecting versions prior to 1.9.8. This security flaw stems from the absence of appropriate nonce validation or CSRF protection mechanisms within the plugin's settings configuration interface.\nA remote attacker can leverage this oversight to execute unauthorized administrative actions by tricking an authenticated administrator into interacting with a malicious, attacker-controlled webpage. Successful exploitation allows the attacker to silently modify the plugin's third-party MailChimp API key settings. Consequently, the impact is significant: all sensitive user registration data, including usernames, email addresses, and membership levels, is redirected to an attacker-controlled MailChimp account. This leads to a total compromise of user data privacy and facilitates potential follow-on attacks such as phishing or identity theft. The vulnerability requires the target administrator to be authenticated during the exploitation attempt, but it effectively bypasses standard security controls by utilizing the administrator's existing session privileges.",
  "technicalDetails": "The vulnerability resides in the administrative settings management module of the Simple Membership MailChimp Integration plugin, specifically where the third-party API integration parameters are saved. The root cause is the failure to implement cryptographic nonce verification (number used once) or any form of anti-CSRF token validation during the processing of POST requests directed at the settings page.\nBecause the plugin fails to verify the origin or intent of the request, an attacker can craft a malicious external HTML document containing a forged form submission. When a logged-in administrator visits the attacker's site, the browser automatically attaches the administrator's session cookies to the forged request, which is then sent to the vulnerable WordPress backend. The plugin, lacking CSRF protection, interprets this request as a legitimate administrative action initiated by the site owner.\nThe attack flow proceeds as follows: 1) The attacker configures a target MailChimp list or account under their control. 2) The attacker crafts an exploit page containing a POST request configured to target the plugin's settings endpoint, with the 'apikey' parameter replaced by the attacker's own credentials. 3) The attacker induces an authenticated WordPress administrator to visit the malicious URL via social engineering or embedded content. 4) The victim's browser executes the POST request with legitimate session privileges. 5) The plugin updates the global settings with the attacker-supplied API key. 6) Subsequent user registrations are processed by the plugin, which now forwards the sensitive PII (Personally Identifiable Information) of newly registered members directly to the attacker's infrastructure.\nThis vulnerability is classified as a low-complexity attack requiring no specialized knowledge of the backend beyond identifying the target URL and parameter names. The post-exploitation impact is severe, as it transforms the legitimate plugin into a data exfiltration vector. The exposure is limited to administrative users; however, because the attack is performed client-side through the victim's session, the network exposure effectively spans any environment where an administrator is active. All versions of the Simple Membership MailChimp Integration plugin prior to 1.9.8 are vulnerable to this manipulation."
}