CVE-2026-0551 Overview
The PPWP – Password Protect Pages plugin for WordPress contains a PHP Object Injection vulnerability affecting all versions up to and including 1.9.18. The flaw stems from unsafe deserialization of the post_protection_roles parameter within class-ppw-passwords.php. Authenticated attackers holding Contributor-level access or above can inject arbitrary PHP objects into the application. The plugin itself does not contain a Property Oriented Programming (POP) chain. Impact occurs only when another installed plugin or theme provides a usable POP chain, at which point attackers can delete arbitrary files, exfiltrate sensitive data, or execute code.
Critical Impact
Authenticated Contributor-level attackers can inject PHP objects that, when combined with a POP chain from another installed component, lead to arbitrary file deletion, data disclosure, or remote code execution.
Affected Products
- PPWP – Password Protect Pages plugin for WordPress, versions up to and including 1.9.18
- Vulnerable file: includes/services/class-ppw-passwords.php
- Vulnerable parameter: post_protection_roles
Discovery Timeline
- 2026-08-23 - CVE-2026-0551 published to NVD
- 2026-08-25 - Last updated in NVD database
Technical Details for CVE-2026-0551
Vulnerability Analysis
The vulnerability is an Insecure Deserialization issue [CWE-502] in the PPWP – Password Protect Pages WordPress plugin. The plugin passes attacker-controlled data from the post_protection_roles request parameter into a PHP deserialization routine without validating that the payload originates from a trusted source. Because PHP unserialize() reconstructs objects and triggers magic methods such as __wakeup() and __destruct(), any class loaded in the current request scope can be instantiated with attacker-controlled properties. The plugin ships no exploitable POP chain on its own. The vulnerability becomes exploitable when another plugin or theme on the site defines classes whose magic methods can be chained into a sensitive operation, such as file deletion, SQL execution, or code evaluation.
Root Cause
The root cause is direct use of PHP deserialization on untrusted input received from an HTTP request parameter. The vulnerable code path at class-ppw-passwords.php line 699 does not enforce a signed or typed data format, and it does not restrict the set of classes that may be reconstructed. Any authenticated user meeting the plugin's capability check reaches the vulnerable sink.
Attack Vector
An attacker authenticates as a Contributor or higher, then submits a crafted serialized PHP object in the post_protection_roles parameter. Once the plugin deserializes the payload, gadget classes provided by other components execute their magic methods. Depending on which POP chain is available, the resulting behavior ranges from arbitrary file deletion to full remote code execution under the web server user.
No verified public proof-of-concept code has been published. Technical detail is available in the WordPress Plugin Code Reference and the Wordfence Vulnerability Analysis.
Detection Methods for CVE-2026-0551
Indicators of Compromise
- Requests to WordPress admin endpoints containing the post_protection_roles parameter with values beginning in O: or a:, characteristic of serialized PHP objects.
- Unexpected file deletions, new PHP files in wp-content/uploads/, or modified plugin and theme files following Contributor-level authenticated activity.
- Web server processes (php-fpm, apache2, www-data) spawning shells, curl, or wget shortly after PPWP plugin requests.
Detection Strategies
- Inspect HTTP POST bodies to PPWP-handled routes for serialized PHP object signatures such as O:\d+:"[A-Za-z_]+".
- Correlate Contributor-level user sessions with subsequent filesystem or database anomalies on WordPress hosts.
- Alert on installed PPWP versions at or below 1.9.18 reported by asset inventory or plugin scanners.
Monitoring Recommendations
- Enable WordPress audit logging for role changes, user creation, and Contributor-level content submissions.
- Monitor outbound network connections from the PHP worker process to unusual destinations.
- Track integrity of wp-content/plugins/, wp-content/themes/, and wp-config.php using file integrity monitoring.
How to Mitigate CVE-2026-0551
Immediate Actions Required
- Update the PPWP – Password Protect Pages plugin to the version published in the fix, referenced in the WordPress Plugin Changeset Update.
- Audit all WordPress user accounts and remove or downgrade unused Contributor, Author, and Editor accounts.
- Review installed plugins and themes for known POP-chain gadgets and remove any that are unmaintained or unnecessary.
Patch Information
The vendor addressed the deserialization sink in changeset 3567221 on the plugin's trunk. Site operators should upgrade past version 1.9.18 to the patched release. Confirm the version reported in wp-admin/plugins.php after upgrade and clear any object or page caches.
Workarounds
- Restrict Contributor-and-above access to trusted users only until the plugin is patched.
- Deploy a Web Application Firewall (WAF) rule that blocks POST bodies containing serialized PHP object patterns targeting PPWP endpoints.
- Temporarily deactivate the PPWP – Password Protect Pages plugin if immediate upgrade is not possible.
# Example WAF pattern to block serialized PHP objects on PPWP requests
# ModSecurity-style rule (adapt to your WAF)
SecRule ARGS:post_protection_roles "@rx ^(O|a):[0-9]+:" \
"id:1002026551,phase:2,deny,status:403,\
msg:'CVE-2026-0551 PPWP PHP object injection attempt'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
