CVE-2025-31840: Simple Fixed Notice CSRF Vulnerability

CVE-2025-31840 Overview

CVE-2025-31840 is a Cross-Site Request Forgery (CSRF) vulnerability in the digireturn Simple Fixed Notice WordPress plugin (dn-cookie-notice). The flaw affects all versions of Simple Fixed Notice up to and including 1.6. The plugin fails to validate the origin of state-changing requests, allowing attackers to forge authenticated requests when a logged-in administrator visits a malicious page. The issue is tracked under CWE-352: Cross-Site Request Forgery and was published to the National Vulnerability Database on April 1, 2025.

Critical Impact

An attacker can trick an authenticated WordPress administrator into performing unintended plugin actions, leading to unauthorized modification of plugin settings.

Affected Products

• digireturn Simple Fixed Notice WordPress plugin (dn-cookie-notice)
• All versions from n/a through 1.6
• WordPress sites with the vulnerable plugin installed and active

Discovery Timeline

• 2025-04-01 - CVE-2025-31840 published to NVD
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-31840

Vulnerability Analysis

The Simple Fixed Notice plugin exposes administrative actions without adequate CSRF protection. WordPress provides a nonce mechanism (wp_nonce_field, check_admin_referer, wp_verify_nonce) to validate that state-changing requests originate from legitimate user interactions. The affected plugin does not properly implement or verify these nonces on one or more request handlers.

Exploitation requires user interaction: an authenticated administrator must visit an attacker-controlled page or click a crafted link while their WordPress session is active. Because the request executes with the administrator's cookies, the server processes it as legitimate. The attacker cannot read responses due to same-origin restrictions, but the write action still succeeds.

The integrity impact is limited to plugin-controlled data. No confidentiality or availability impact is associated with this issue based on the reported metrics.

Root Cause

The root cause is missing or insufficient anti-CSRF token validation on plugin request handlers. Handlers accept requests based solely on session cookies without verifying a per-request nonce, referer header, or equivalent origin control. This maps directly to CWE-352.

Attack Vector

The attack vector is network-based and requires user interaction. A typical exploitation flow proceeds as follows:

1. The attacker hosts a page containing an auto-submitting HTML form or an image tag that issues a request to the vulnerable plugin endpoint on the target WordPress site.
2. An authenticated WordPress administrator visits the attacker-controlled page while logged into the target site.
3. The browser attaches session cookies to the cross-origin request.
4. The plugin processes the request as if the administrator initiated it, applying the attacker-supplied changes.

Refer to the Patchstack WordPress Vulnerability Report for the underlying advisory details.

Detection Methods for CVE-2025-31840

Indicators of Compromise

• Unexpected changes to Simple Fixed Notice plugin settings without corresponding administrator activity in audit logs
• Referer headers in web server logs pointing to external, unrelated domains for wp-admin POST requests targeting the plugin
• Administrator sessions performing plugin configuration changes immediately after browsing external sites

Detection Strategies

• Review WordPress audit logs for plugin option modifications that lack a corresponding administrator-initiated session workflow
• Correlate HTTP request logs to identify POST requests to plugin endpoints with third-party referers or missing nonces
• Deploy a Web Application Firewall (WAF) rule to flag wp-admin state-changing requests that lack a valid _wpnonce parameter

Monitoring Recommendations

• Enable a WordPress activity logging plugin to track option and settings changes with user attribution
• Monitor outbound administrator browsing sessions for known malicious domains that may host CSRF payloads
• Alert on anomalous configuration writes to wp_options entries associated with dn-cookie-notice

How to Mitigate CVE-2025-31840

Immediate Actions Required

• Deactivate the Simple Fixed Notice plugin until a patched version above 1.6 becomes available
• Restrict WordPress administrator accounts from browsing untrusted sites in the same session used for site administration
• Enforce short administrator session lifetimes and require re-authentication for sensitive actions

Patch Information

At the time of publication, no fixed version has been listed for Simple Fixed Notice beyond 1.6. Monitor the Patchstack advisory and the plugin's WordPress.org listing for an official update.

Workarounds

• Remove the plugin entirely if a business-critical requirement does not exist for its functionality
• Deploy a WAF rule that blocks POST requests to wp-admin endpoints missing a valid _wpnonce value or presenting a cross-origin referer
• Apply the principle of least privilege by limiting the number of accounts with administrator capabilities

# Example WAF rule concept: block cross-origin POSTs to wp-admin without a nonce
# ModSecurity-style pseudo-rule
SecRule REQUEST_METHOD "@streq POST" \
  "chain,deny,status:403,id:1003184,msg:'Potential CSRF against wp-admin'"
  SecRule REQUEST_URI "@contains /wp-admin/" "chain"
    SecRule &ARGS:_wpnonce "@eq 0"