UEditor Arbitrary File Upload Scanner

UEditor is a popular open-source rich text editor developed by Baidu. It is widely integrated into web applications and content management systems to provide users with a feature-rich WYSIWYG editing experience. Due to its flexibility and ease of use, UEditor is commonly adopted by organizations and developers to enable the creation and management of formatted content. However, as with many web-facing components, its exposure to user input and file handling mechanisms necessitates stringent security practices to prevent potential exploitation.

The Arbitrary File Upload vulnerability in UEditor stems from inadequate validation of user-supplied file uploads. Specifically, the flaw exists in the server-side upload handling script, which fails to enforce strict checks on file types and content. As a result, remote attackers can upload arbitrary files, including executable PHP scripts, to the server. Once uploaded, these files can be accessed and executed, leading to a complete compromise of the web application or server environment. The vulnerability is particularly severe because it provides an avenue for attackers to achieve remote code execution (RCE), escalate privileges, and establish persistent backdoors.

Technically, the issue arises from insufficient input sanitization and improper configuration of the upload endpoint (commonly at '/ueditor/net/controller.ashx' or equivalent). Attackers can craft malicious multipart/form-data HTTP requests that bypass file extension filters by employing techniques such as double extensions (e.g., 'shell.php.jpg') or manipulating Content-Type headers. Once uploaded, the malicious file can be directly accessed via the web root, granting attackers the ability to execute arbitrary commands on the server.

The impact of successfully exploiting this vulnerability includes unauthorized server access, data exfiltration, installation of malware, and lateral movement within the compromised network. It underscores the critical importance of implementing robust upload validation mechanisms, including strict MIME type checks, server-side extension whitelisting, and isolating uploaded files from executable directories.