WordPress User Frontend Plugin Deserialization Vulnerability (CVE-2026-5127)

The User Frontend: AI Powered Frontend Posting, User Directory, Profile, Membership & User Registration plugin for WordPress, versions up to and including 4.3.1, contains a deserialization of untrusted data vulnerability (CVE-2026-5127). This flaw stems from the lack of proper input validation and type checking applied to the wpuf_files parameter during form submission, coupled with the usage of maybe_unserialize() when post content is displayed. An authenticated attacker with subscriber-level privileges can exploit this vulnerability by injecting arbitrary PHP objects. Successful exploitation could lead to arbitrary code execution, deletion of arbitrary files, or other malicious actions, contingent upon the presence of a suitable POP chain on the target system. This vulnerability poses a significant risk to WordPress sites utilizing the affected plugin, potentially allowing attackers to gain complete control over the compromised website.

Attack Chain

1. Attacker authenticates to the WordPress site with subscriber-level or higher privileges.
2. Attacker crafts a malicious HTTP POST request targeting a form submission endpoint. This request includes a serialized PHP object within the wpuf_files parameter.
3. The WordPress application receives the POST request and processes the wpuf_files parameter without proper validation or sanitization.
4. The maybe_unserialize() function is called on the wpuf_files parameter’s value, unconditionally deserializing the attacker-controlled data.
5. If a suitable POP chain exists within the WordPress installation or installed plugins, the deserialization process triggers the execution of arbitrary code.
6. The attacker’s code gains execution within the context of the web server.
7. The attacker can then perform malicious actions such as creating administrative accounts, injecting web shells, or deleting critical files.
8. The attacker establishes persistence and maintains control over the compromised WordPress site.

Impact

Successful exploitation of CVE-2026-5127 can result in complete compromise of the affected WordPress website. Attackers can gain administrative access, inject malicious code into the site’s files and database, deface the website, steal sensitive data, or use the compromised site to launch further attacks. The impact depends on the privileges of the compromised account and the presence of a suitable POP chain. Given the widespread use of WordPress and the popularity of the affected plugin, this vulnerability could potentially impact thousands of websites.

Recommendation

• Upgrade the “User Frontend: AI Powered Frontend Posting, User Directory, Profile, Membership & User Registration” plugin to a version greater than 4.3.1 to patch CVE-2026-5127.
• Deploy the provided Sigma rule “Detect CVE-2026-5127 Exploitation Attempt via wpuf_files Parameter” to monitor for malicious POST requests containing serialized PHP objects in the wpuf_files parameter.
• Review WordPress access logs for suspicious POST requests to form submission endpoints, focusing on those with unusually long or complex wpuf_files parameters to identify potential exploitation attempts (webserver logs).