CVE-2026-4409: WordPress Plugin Auth Bypass Vulnerability

CVE-2026-4409 Overview

CVE-2026-4409 affects the Subscribe To Comments Reloaded plugin for WordPress in all versions up to and including 240119. The plugin leaks a global secret key on public post pages and uses a weak hash generation algorithm to produce authorization keys. Unauthenticated attackers can extract the leaked key from any public post and forge valid authorization tokens. With forged tokens, attackers manage comment subscription preferences for arbitrary users without their consent. The issue is classified under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.

Critical Impact

Unauthenticated attackers can forge per-user authorization keys and modify comment subscription preferences for any subscriber on the affected WordPress site.

Affected Products

• WordPress sites running the Subscribe To Comments Reloaded plugin
• Plugin versions up to and including 240119
• All earlier releases of the Subscribe To Comments Reloaded plugin

Discovery Timeline

• 2026-05-05 - CVE-2026-4409 published to NVD
• 2026-05-05 - Last updated in NVD database

Technical Details for CVE-2026-4409

Vulnerability Analysis

The Subscribe To Comments Reloaded plugin generates per-user authorization keys to allow subscribers to manage their comment subscription preferences without logging in. These keys are produced using a weak hashing algorithm seeded with a global secret. The plugin then renders that secret into HTML output served on public post pages, as visible in the plugin template code and the main plugin file. The hash construction logic is defined in the plugin utility code. Because the secret is exposed and the hash function is reversible by recomputation, an attacker can derive valid keys for any registered subscriber email.

Root Cause

The root cause is twofold: the global secret key is included in unauthenticated page output, and the authorization key is derived from a predictable hash algorithm. Once the secret is recovered, key forgery becomes deterministic. Additional context is available in the Wordfence vulnerability report.

Attack Vector

An unauthenticated attacker fetches any public post page on a vulnerable site and parses the rendered template to recover the global secret. The attacker then computes the weak hash for a target email address to produce a forged authorization token. Submitting that token to the subscription management endpoint allows arbitrary modification of another user's subscription preferences.

Detection Methods for CVE-2026-4409

Indicators of Compromise

• Unexpected GET requests to public posts followed by requests to the plugin's user management endpoint with srk or similar key parameters.
• Subscription management actions performed for email addresses that do not correlate with authenticated sessions or recent comment activity.
• High volumes of subscription preference changes originating from a small set of source IP addresses.

Detection Strategies

• Inspect web server access logs for repeated access to the plugin's subscription management URL with varying email parameters.
• Compare the user-agent and IP distribution of requests to the plugin endpoints against legitimate subscriber traffic baselines.
• Alert on responses from the plugin endpoint that confirm successful preference changes without a corresponding authenticated session.

Monitoring Recommendations

• Forward WordPress and web server logs to a centralized analytics platform and build queries for plugin endpoint abuse.
• Track plugin version inventory across hosted WordPress sites and flag any instance running version 240119 or earlier.
• Monitor outbound notification emails from WordPress for spikes in subscription change confirmations.

How to Mitigate CVE-2026-4409

Immediate Actions Required

• Update the Subscribe To Comments Reloaded plugin to a version released after 240119 that addresses the leaked secret and weak hash logic.
• If a patched version is unavailable, deactivate and remove the plugin until a fix is published.
• Audit existing comment subscriptions for entries that subscribers did not authorize and remove suspicious records.

Patch Information

Review the Wordfence vulnerability report for the latest fixed version guidance. Apply WordPress plugin updates through the administrative dashboard or via wp-cli to ensure all sites are remediated.

Workarounds

• Restrict access to the plugin's subscription management endpoint at the web application firewall (WAF) layer until a patch is applied.
• Temporarily disable the public-facing subscription form rendered by the plugin to prevent secret leakage in page output.
• Rotate the plugin's global secret after upgrading to invalidate any previously forged authorization keys.

# Configuration example
wp plugin update subscribe-to-comments-reloaded
wp plugin deactivate subscribe-to-comments-reloaded   # if no patch is available