Appwrite < 2.0.0 Argument Injection via providerRootDirectory Parameter

Appwrite before 2.0.0 contains an argument injection vulnerability that allows authenticated users with functions.write or sites.write permissions to execute arbitrary commands by injecting TAB characters into the providerRootDirectory parameter used to construct GNU tar commands. The application uses escapeshellcmd instead of escapeshellarg and fails to quote the parameter, allowing TAB characters to survive sanitization and be interpreted as argument separators, enabling injection of arbitrary GNU tar arguments such as --checkpoint-action=exec to achieve remote code execution as the builds worker process user.