0x00 unsafe file upload vulnerability overview of unsafe file upload vulnerability Overview
File upload function are common in web applications, such as many sites registered when the need to upload picture, upload attachments, and so on.
When the user clicks the Upload button, the background will upload the file to determine whether such is the specified type, extension, size, etc., and then rename the directory after storage in accordance with the format specified design.
Such as uploading picture jpg png upload documents dox
If the background of the uploaded files without any judgment or judgment of the security condition is not stringent enough, an attacker could upload a malicious file, such as a word Trojan, causing back-end server is webshell.
So, when designing a file upload function, be sure to strict security file passed in. For example:
- Verify the file type, extension, size;
- uploading verification documents;
- the file certain complex renaming;
- Do not expose the path after file upload;
- and so on ...
0x01 Client check