Description

Unauthenticated PHP Object Injection in Hash Form <= 1.4.1 versions.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-08-27T10:16:38.530Z",
  "pubdate": "2026-08-27T10:16:38.530Z",
  "executiveSummary": "The Hash Form plugin for WordPress, specifically versions 1.4.1 and below, contains a critical security vulnerability involving unauthenticated PHP Object Injection.\nThe vulnerability arises from the improper handling of user-supplied input that is subsequently passed to the unserialize() function in PHP.\nBy crafting a malicious serialized object, an unauthenticated attacker can manipulate the application's state, leading to severe security consequences.\nPotential impacts include Remote Code Execution (RCE), arbitrary file deletion, or sensitive data exposure, depending on the availability of 'gadget chains' present within the application environment, including the WordPress core or other installed plugins.\nThis vulnerability is classified as critical because it does not require prior authentication or elevated privileges, allowing any remote attacker with network access to the target installation to trigger the exploit.\nThe risk implication is absolute, as successful exploitation can lead to a full compromise of the underlying web server and the hosted WordPress site.",
  "technicalDetails": "The core vulnerability is an insecure deserialization flaw located within the Hash Form plugin codebase. The application accepts serialized data from user-controllable input fields without performing adequate validation or sanitization prior to passing the data to the PHP unserialize() function.\nIn PHP, the unserialize() function reconstructs stored values from a serialized string. When this function processes untrusted input, an attacker can supply a specially crafted object that, upon instantiation, triggers unintended behavior through PHP magic methods such as __wakeup(), __destruct(), or __toString().\nThe attack flow begins when an unauthenticated attacker identifies a public-facing endpoint or input vector processed by the Hash Form plugin that expects serialized data. The attacker then constructs a malicious payload utilizing existing classes defined within the application or its dependencies (gadget chains).\nUpon transmission of the malicious payload, the application invokes unserialize() on the input. This forces the application to instantiate the attacker-controlled object. If the object contains magic methods that perform dangerous operations—such as file manipulation, system command execution, or dynamic property assignment—those operations are executed within the security context of the web server process.\nBecause the vulnerability is unauthenticated, there are no requirements for a valid session or administrative privileges, making this an highly accessible attack vector over the network. The scope of the post-exploitation impact is limited only by the permissions of the PHP process and the presence of reachable gadget chains within the environment.\nThe vulnerability affects Hash Form versions 1.4.1 and earlier. Successful exploitation typically results in Remote Code Execution (RCE), where the attacker gains the ability to execute arbitrary system commands, potentially leading to a full system compromise, lateral movement within the network, or persistent backdoor installation."
}