CVE-2026-59539: Paid Member Subscriptions IDOR Vulnerability

CVE-2026-59539 Overview

CVE-2026-59539 is an Insecure Direct Object Reference (IDOR) vulnerability affecting the Paid Member Subscriptions WordPress plugin in versions up to and including 3.0.7. The flaw allows authenticated subscriber-level users to manipulate object identifiers and access or modify resources belonging to other accounts. The issue is tracked under CWE-639: Authorization Bypass Through User-Controlled Key. Patchstack published the initial advisory documenting the weakness in the plugin's object reference handling.

Critical Impact
Authenticated subscribers can tamper with subscription records tied to other users, resulting in an integrity impact on membership data managed by the plugin.

Affected Products

Paid Member Subscriptions WordPress plugin versions <= 3.0.7
WordPress sites offering paid membership, subscription, or restricted-content functionality via the plugin
Any deployment allowing subscriber-level account registration on the affected plugin versions

Discovery Timeline

2026-07-27 - CVE-2026-59539 published to the National Vulnerability Database
2026-07-27 - Last updated in NVD database

Technical Details for CVE-2026-59539

Vulnerability Analysis

The vulnerability resides in the Paid Member Subscriptions plugin's handling of user-supplied object identifiers. The plugin accepts identifiers referencing subscription objects but fails to verify that the requesting account owns or has permission to modify the referenced resource. An authenticated user at the subscriber role can therefore act on records belonging to other members. The advisory classifies the impact as integrity-focused, with confidentiality and availability unaffected.

Root Cause

The root cause is missing authorization enforcement on object identifiers passed through plugin request handlers. The application trusts client-supplied keys, such as subscription or member IDs, without cross-referencing the authenticated session against the resource owner. This pattern maps directly to CWE-639, where access control decisions depend on user-controlled input rather than server-side ownership checks.

Attack Vector

Exploitation requires a valid subscriber account, which is often obtainable through open registration on membership sites. The attacker submits crafted requests to plugin endpoints while substituting the target object identifier with one belonging to another user. Because the vulnerability is exposed over the network and requires no user interaction, automated tools can enumerate identifiers and modify data at scale. See the Patchstack Vulnerability Report for technical details.

Detection Methods for CVE-2026-59539

Indicators of Compromise

Unexpected modifications to subscription or member records that do not correspond to the owning user's session activity
Subscriber accounts issuing HTTP requests to Paid Member Subscriptions endpoints with sequentially varying numeric identifiers
Membership data changes originating from IP addresses inconsistent with the resource owner's normal geography

Detection Strategies

Review WordPress and web server access logs for repeated POST or GET requests to plugin action handlers with iterating id, subscription_id, or member_id parameters
Correlate authenticated user IDs against the object identifiers touched in each request to identify cross-account references
Enable audit logging via a WordPress security plugin to capture subscription state changes with actor attribution

Monitoring Recommendations

Alert on subscriber-role accounts generating a high volume of requests to paid-member-subscriptions endpoints within short time windows
Monitor database write operations against subscription tables for updates where the acting user does not match the record owner
Track new account registrations followed by immediate API interaction with plugin endpoints

How to Mitigate CVE-2026-59539

Immediate Actions Required

Upgrade the Paid Member Subscriptions plugin to a version above 3.0.7 as soon as the vendor-published patched release is available
Audit existing subscription and member records for unauthorized modifications made since the plugin was installed
Restrict or disable open subscriber registration until the plugin is patched

Patch Information

Refer to the Patchstack Vulnerability Report for the fixed version and update instructions. Apply the vendor update through the WordPress plugin manager or via a controlled deployment pipeline, then verify the installed version is greater than 3.0.7.

Workarounds

Deploy a Web Application Firewall (WAF) rule to block subscriber requests that reference object identifiers outside the authenticated user's owned records
Temporarily disable the Paid Member Subscriptions plugin on production sites that cannot be patched immediately
Rotate session tokens and force re-authentication for all subscriber accounts after applying the update

bash

# Configuration example: verify installed plugin version via WP-CLI
wp plugin get paid-member-subscriptions --field=version
wp plugin update paid-member-subscriptions