Description

Contributor PHP Object Injection in RTMKit <= 2.1.5 versions.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-03T17:17:25.547Z",
  "pubdate": "2026-09-03T17:17:25.547Z",
  "executiveSummary": "RTMKit versions 2.1.5 and earlier are susceptible to a PHP Object Injection vulnerability, categorized under CWE-502: Deserialization of Untrusted Data.\nThis vulnerability exists due to the improper handling of serialized user-supplied input before processing it via PHP's unserialize() function.\nAn authenticated attacker with Contributor-level privileges or higher can leverage this flaw to instantiate arbitrary PHP objects within the application scope.\nSuccessful exploitation allows for a range of malicious outcomes, including Remote Code Execution (RCE), arbitrary file deletion, or sensitive data access, depending on the available gadget chains present within the application's codebase or included dependencies.\nThe risk is considered critical, as it bypasses standard input validation mechanisms and allows the attacker to manipulate the internal state of the application.\nThe vulnerability requires an authenticated session, but given the widespread accessibility of Contributor accounts in many WordPress-based environments, it presents a significant threat to site integrity and server security.",
  "technicalDetails": "The vulnerability originates in RTMKit versions <= 2.1.5, where user-controllable input is passed directly to the PHP unserialize() function without adequate sanitization or integrity verification.\nPHP Object Injection occurs when an application deserializes untrusted data that has been manipulated by an attacker to include serialized objects of arbitrary classes available in the application's execution context.\nWhen the unserialize() function is executed on the malicious payload, PHP automatically attempts to instantiate the specified class. If the class includes magic methods such as __wakeup(), __destruct(), or __toString(), the attacker can trigger these methods with controlled property values.\nBy chaining these magic methods with existing 'gadgets'—classes already defined in the application or its bundled libraries that perform dangerous operations—an attacker can achieve Remote Code Execution (RCE).\nThe attack flow proceeds as follows: 1) The attacker identifies an input vector in RTMKit that accepts serialized data; 2) The attacker crafts a malicious serialized string containing the payload representing a target gadget chain; 3) The attacker submits this payload via the vulnerable parameter; 4) The server-side application processes the input through unserialize(); 5) The application triggers the magic methods within the gadget chain, executing arbitrary code or performing unauthorized operations under the security context of the web server process.\nBecause the vulnerability is triggered during the deserialization process, it effectively circumvents traditional input filtering or type-checking mechanisms, as the exploitation is focused on the object instantiation phase rather than the content of the data itself.\nThe impact is determined by the complexity of the gadget chain found within the RTMKit environment. In many configurations, this allows for full application compromise, unauthorized modification of the site configuration, or the execution of system-level commands if the web server process permissions allow.\nThis issue highlights a failure to adhere to secure coding practices regarding the handling of serialized data. The lack of integrity checks, such as Message Authentication Codes (HMAC) or digital signatures, on the serialized data allows attackers to alter object states and force the application into unintended execution paths."
}