CVE-2025-31876: Payday Plugin Auth Bypass Vulnerability

CVE-2025-31876 Overview

CVE-2025-31876 is a missing authorization vulnerability in the gunnarpayday Payday plugin for WordPress. The flaw affects all versions up to and including 3.3.18. Attackers can exploit incorrectly configured access control security levels to reach functionality that should require authentication or elevated privileges. The vulnerability is categorized under [CWE-862] (Missing Authorization) and can be triggered remotely over the network without user interaction. Because the scope changes when the flaw is exploited, an attacker acting through the vulnerable plugin can impact resources beyond its own security boundary. The issue is tracked by Patchstack in the WordPress plugin vulnerability database.

Critical Impact
Unauthenticated network attackers can reach protected Payday plugin functionality and expose limited confidential data on affected WordPress sites.

Affected Products

gunnarpayday Payday WordPress plugin versions up to and including 3.3.18
WordPress sites running the Payday plugin with default access control configuration
Any WordPress installation that has not applied the vendor patch above 3.3.18

Discovery Timeline

2025-04-03 - CVE-2025-31876 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-31876

Vulnerability Analysis

The Payday plugin exposes functionality without properly verifying the requester's authorization level. The plugin implements access control checks, but the checks are configured at the wrong security level, so requests that should be rejected are honored. An unauthenticated attacker can invoke protected actions by sending crafted HTTP requests to endpoints registered by the plugin. Because the vulnerable code path runs inside WordPress, the impact crosses component boundaries and can reach data outside the plugin itself. Confidentiality is affected at a limited level, while integrity and availability are not directly impacted according to the published CVSS metrics.

Root Cause

The root cause is a missing or misplaced authorization check ([CWE-862]) in one or more handlers registered by the Payday plugin. The plugin relies on incorrectly configured access control security levels, meaning capability or nonce checks either do not run or run against a permission tier that permits unauthenticated users. WordPress plugins commonly hit this class of bug when using admin-post.php, admin-ajax.php, or REST route handlers without current_user_can() or equivalent capability validation.

Attack Vector

Exploitation is performed remotely over HTTP or HTTPS against a vulnerable WordPress site. An attacker sends a request to a plugin-controlled endpoint that omits or bypasses authorization. Because no privileges and no user interaction are required, the request can originate from any internet-connected host that can reach the WordPress site. See the Patchstack advisory for the Payday plugin broken access control vulnerability for technical details on the affected endpoints.

No verified public proof-of-concept code is available. The vulnerability class allows an attacker to invoke plugin actions by issuing standard HTTP requests to registered plugin routes without valid authentication cookies or nonces.

Detection Methods for CVE-2025-31876

Indicators of Compromise

Unauthenticated HTTP requests to Payday plugin endpoints under /wp-admin/admin-ajax.php, /wp-admin/admin-post.php, or /wp-json/ routes registered by the plugin
Requests to plugin actions from source IPs that never completed a WordPress login flow
Anomalous access patterns to Payday functionality outside normal administrator workflows

Detection Strategies

Inventory WordPress installations and identify sites running Payday <= 3.3.18 using plugin version scanners or the WordPress REST API
Review web server access logs for POST or GET requests to Payday-registered endpoints that lack authenticated session cookies
Correlate WordPress audit logs with web server logs to identify plugin actions performed without a corresponding authenticated user session

Monitoring Recommendations

Enable a WordPress audit logging plugin to record plugin action invocations and administrative changes
Forward WordPress and web server logs to a centralized log platform for retention and query
Alert on repeated requests to Payday endpoints from a single external source within a short interval

How to Mitigate CVE-2025-31876

Immediate Actions Required

Update the Payday plugin to a version later than 3.3.18 as soon as the vendor releases a fixed build
If a patched version is not yet installed, deactivate and remove the Payday plugin from affected WordPress sites
Restrict access to /wp-admin/ and plugin-specific endpoints using a web application firewall or IP allow list
Review WordPress user accounts and content for unauthorized changes made since the plugin was installed

Patch Information

Refer to the Patchstack advisory for the Payday WordPress plugin for the fixed version and remediation guidance. Apply the vendor's updated plugin release through the WordPress plugin manager or by replacing the plugin files directly.

Workarounds

Block external requests to Payday endpoints at a reverse proxy or WAF until the plugin is updated
Enforce HTTP authentication on /wp-admin/admin-ajax.php and /wp-admin/admin-post.php for unauthenticated visitors where feasible
Reduce the plugin's exposure by taking the site offline or placing it behind a maintenance page if the plugin cannot be removed

bash

# Example: block unauthenticated access to Payday plugin endpoints via nginx
location ~* /wp-content/plugins/payday/ {
    deny all;
    return 403;
}