Unrestricted File Upload

high Web App Scanning Plugin ID 114283

Language:

Synopsis

Description

Unrestricted file upload vulnerability occurs when the application suffers from a lack of validation of files being uploaded to its filesystem. When an attacker is able to upload files not matching the application expectations in terms of names, type, content or size, it could lead to various issues such as arbitrary files overwrite, denial of service or even remote code execution.

Note that this plugin requires the 'File Upload' assessment option enabled in the scan configuration.

Solution

Ensure that all controls apply on the file being uploaded : - Implement an allowlist of the accepted file extensions and ensure that it cannot be bypassed. - Ensure that the permissions applied on the uploaded file are set to the strict minimum and prevents execution. - Ensure that the filename does not contain any substring that could be used by the function writing the file as a directory traversal pattern. - Rename the uploaded files to avoid overwriting local system files. - Ensure that the file size is acceptable and not too big, to avoid service disruption due to disk space consumption or overbilling when using cloud services.