CVE-2026-42723 in CleanSkin Plugin
Summary
by MITRE • 10/10/2026
Unauthenticated PHP Object Injection in CleanSkin <= 1.5.0 versions.
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Analysis
by VulDB Data Team • 10/11/2026
The vulnerability identified as an unauthenticated PHP object injection flaw within CleanSkin versions prior to or equal to 1.5.0 represents a critical security deficiency that allows attackers to execute arbitrary code on the target server without requiring valid credentials. This type of vulnerability arises from the application's failure to properly validate and sanitize user-supplied input before it is passed to PHP’s unserialize function, which is commonly used for deserializing objects stored in sessions or cookies. When an attacker provides a crafted serialized string containing maliciously constructed object instances with exploitable magic methods such as __destruct, __wakeup, or __toString, the application inadvertently instantiates these objects and executes their associated logic during the unserialization process. This mechanism bypasses standard authentication controls because the vulnerability is triggered by manipulating data structures that are often automatically processed upon page load or specific API interactions, thereby granting remote code execution capabilities to any internet-facing user with network access to the vulnerable endpoint.
From a technical perspective, this flaw aligns closely with Common Weakness Enumeration identifier CWE-502, which describes Deserialization of Untrusted Data. The root cause typically involves the use of insecure deserialization practices where the application trusts input from unverified sources or fails to implement integrity checks such as cryptographic signing before processing serialized objects. In the context of CleanSkin, a WordPress theme, this likely occurs through parameters passed via GET requests, POST data, or cookies that are directly fed into PHP functions responsible for object reconstruction. The attacker can leverage known classes within the application’s dependency chain or utilize gadget chains—sequences of existing methods in included libraries—to achieve arbitrary function calls. This capability effectively transforms a simple input validation error into a full system compromise, allowing the adversary to read sensitive files, modify database contents, install backdoors, or pivot further into the internal network depending on the privileges under which the web server process operates.
The operational impact of this vulnerability is severe and immediate. An unauthenticated attacker can achieve Remote Code Execution (RCE), leading to a complete compromise of the underlying operating system hosting the WordPress installation. This results in unauthorized access to confidential data, including user credentials, database contents, and proprietary site configurations. Furthermore, the compromised server may be utilized as part of a botnet for distributed denial-of-service attacks or used to distribute malware to visitors accessing the infected website. The presence of such a vulnerability significantly degrades trust in the platform and exposes organizations to regulatory penalties under frameworks like GDPR if personal data is exfiltrated due to this exploit vector.
Mitigation strategies must prioritize immediate remediation through software updates. Administrators should upgrade CleanSkin to version 1.5.1 or later, where the developers have presumably implemented proper input validation and restricted deserialization operations to trusted sources only. In cases where upgrading is not immediately feasible, temporary mitigations include disabling PHP’s unserialize function if it is not strictly required for core functionality, although this may break legitimate features. Additionally, implementing strict Content Security Policy headers and ensuring that session cookies are marked with HttpOnly and Secure flags can reduce the attack surface by limiting how client-side scripts interact with sensitive data. Long-term architectural improvements should involve adopting secure coding practices such as using JSON instead of PHP serialized objects for data exchange, validating all inputs against a whitelist of expected values, and employing static application security testing tools to detect insecure deserialization patterns during development.
This vulnerability is categorized under the MITRE ATT&CK framework technique T1059, specifically Command and Scripting Interpreter: PHP, as it enables attackers to execute arbitrary commands via the PHP environment. It also relates to T1190, Exploit Public-Facing Application, highlighting its nature as a remote exploit targeting publicly accessible software components. Security teams should monitor for indicators of compromise associated with this specific gadget chain or unusual outbound network connections originating from the web server directory structure where CleanSkin is installed. Regular vulnerability scanning and penetration testing are essential to identify similar deserialization flaws in other plugins or themes that may share common libraries, ensuring a holistic defense against object injection attacks across the entire WordPress ecosystem.