CVE-2026-0551 in PPWP Plugin
Summary
by MITRE • 08/23/2026
The PPWP – Password Protect Pages plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 1.9.18 via deserialization of untrusted input from the 'post_protection_roles' vulnerable parameter. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject a PHP Object. No known POP chain is present in the vulnerable software, which means this vulnerability has no impact unless another plugin or theme containing a POP chain is installed on the site. If a POP chain is present via an additional plugin or theme installed on the target system, it may allow the attacker to perform actions like delete arbitrary files, retrieve sensitive data, or execute code depending on the POP chain present.
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Analysis
by VulDB Data Team • 08/23/2026
The PPWP – Password Protect Pages plugin for WordPress contains a critical PHP Object Injection vulnerability affecting all versions up through 1.9.18. This flaw stems from the improper deserialization of untrusted input provided via the post_protection_roles parameter. In secure software design, data structures should be serialized only when necessary and must never accept raw user-supplied data for direct deserialization without rigorous validation or type checking. By allowing authenticated users to influence this specific parameter which is then passed directly into a PHP unserialize function, the application creates an entry point where attackers can manipulate the internal state of the object graph during runtime. This class of vulnerability falls under CWE-502 Deserialization of Untrusted Data and represents a significant risk in environments where plugins handle complex configuration states that rely on serialized objects for persistence or logic execution.
The severity of this vulnerability is heavily dependent on the broader ecosystem of the targeted WordPress installation because no known PHP Object Injection POP chain exists within the PPWP plugin itself. A POP chain requires specific gadget classes with magic methods such as __destruct, __wakeup, or __toString that can be chained together to achieve arbitrary code execution or other malicious outcomes. Since the vulnerable plugin lacks these internal gadgets, an attacker cannot exploit this flaw in isolation to gain immediate control over the server. However, WordPress sites typically operate with multiple plugins and themes active simultaneously. If any of these additional components contain exploitable gadget chains, the injection point provided by PPWP can serve as a bridge for attackers to trigger those external payloads. This scenario highlights how vulnerabilities in one component can amplify risks across an entire application stack when shared resources like serialization mechanisms are involved.
Exploitation requires authenticated access with at least Contributor-level privileges or higher within WordPress. While this restricts the attack surface compared to unauthenticated exploits, it remains a serious concern for sites where low-privilege users might be trusted or where account compromise is feasible through other means such as credential stuffing or phishing. Once an attacker successfully injects a crafted PHP object into the post_protection_roles parameter, they can potentially manipulate how WordPress handles page protection settings. If a compatible POP chain exists in another installed plugin or theme, this manipulation could lead to severe operational impacts including arbitrary file deletion which may disrupt service availability, retrieval of sensitive data such as database credentials stored in configuration files, or remote code execution that grants full control over the web server environment. These outcomes align with techniques observed in ATT&CK framework categories related to persistence and privilege escalation via application layer vulnerabilities.
Mitigation strategies should prioritize immediate remediation by upgrading the PPWP plugin to a version later than 1.9.18 where this deserialization flaw has been addressed through input validation or replacement of unsafe serialization calls. In cases where an upgrade is not immediately possible, administrators can implement web application firewall rules to detect and block requests containing suspicious serialized payloads targeting the post_protection_roles parameter. Additionally, enforcing strict least-privilege principles for user accounts reduces the likelihood that an attacker will obtain the necessary Contributor-level access required to trigger this vulnerability. Regular audits of installed plugins are also recommended to identify any components with known POP chains or outdated dependencies that could be leveraged in conjunction with this injection point. Maintaining a clean and minimal plugin environment significantly lowers the probability of successful exploitation by reducing the availability of exploitable gadgets within the application context.