CVE-2026-81780 in Hash Form Plugin
Summary
by MITRE • 09/01/2026
Unauthenticated Arbitrary File Upload in Hash Form <= 1.4.2 versions.
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Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified as an unauthenticated arbitrary file upload flaw within Hash Form versions prior to 1.4.2 represents a critical security deficiency that allows attackers to execute remote code on the targeted server without requiring valid credentials. This type of vulnerability is fundamentally rooted in insufficient input validation and inadequate access control mechanisms during the file handling process. When users interact with the plugin's frontend forms, which are designed for collecting user data such as contact information or survey responses, the system fails to properly verify the authenticity of the requestor or restrict the types of files that can be uploaded through these interfaces. Consequently, an attacker who is not logged into the WordPress environment can exploit this weakness by crafting a malicious HTTP POST request containing a specially crafted file payload.
From a technical perspective, the core issue lies in how the application processes incoming file uploads. The software likely relies on basic MIME type checks or filename extensions to determine validity, which are easily bypassed using common evasion techniques such as double extension manipulation or content-type spoofing. Furthermore, the absence of authentication requirements means that this attack vector is accessible to any internet user with network connectivity to the vulnerable site. Once a malicious file, typically a PHP web shell, is successfully uploaded to a publicly accessible directory within the WordPress installation, it becomes executable by the web server. This transforms the upload mechanism from a benign data collection tool into a direct pathway for system compromise.
The operational impact of this vulnerability is severe and multifaceted. Upon successful exploitation, an attacker gains full control over the underlying operating system through the context of the web service user account. This level of access enables the execution of arbitrary commands, leading to complete site defacement, data exfiltration from associated databases, or the use of the compromised server as a pivot point for further attacks against internal network resources. Attackers may also install persistent backdoors, launch distributed denial-of-service attacks using the infected machine's bandwidth, or spread malware to visitors who access the compromised website. The lack of authentication makes this vulnerability particularly dangerous in public-facing environments where automated scanning tools can rapidly identify and exploit instances across thousands of servers simultaneously.
This flaw aligns with CWE-434, which describes Unrestricted Upload of File with Dangerous Type, as well as CWE-79, known as Cross-Site Scripting if the uploaded file is rendered directly in a browser context without sanitization. In terms of the MITRE ATT&CK framework, this vulnerability facilitates initial access through web application exploits and allows for command-and-control operations via the deployed web shell. The attack sequence typically involves reconnaissance to identify vulnerable installations, followed by exploitation using crafted requests that bypass validation logic, resulting in remote code execution.
Mitigation strategies must prioritize immediate remediation due to the high severity of this issue. Administrators running Hash Form versions 1.4.2 or earlier should upgrade to version 1.4.3 or later immediately, as these newer releases include patches for the file upload validation logic and enforce stricter access controls on form submission endpoints. In cases where upgrading is not immediately feasible, temporary mitigations may involve restricting write permissions on directories used by the plugin to prevent new files from being created there. Additionally, implementing a Web Application Firewall can help detect and block requests containing suspicious file extensions or malformed multipart data structures associated with upload exploits. Regular security audits and monitoring of server logs for unusual activity patterns related to file uploads are also recommended to ensure ongoing protection against similar threats.