The Malware Audit
In Ubuntu Linux, files do not rely on extensions (like .exe or .bat) to dictate whether they can be run as a program. Instead, Linux relies entirely on internal file permissions (specifically, the execute bit). This means a malicious payload could be disguised as a harmless text file (notes.txt), but if the execute bit is set, the system will attempt to run it as a script. To secure a server—particularly directories where users are allowed to upload files, like /var/www/uploads/—you must audit the filesystem for any file that is mathematically capable of execution.
Using the find Command with -executable
The Linux find command utilizes the -executable flag to exclusively search for files that possess the execution permission bit for the current user.
- Open your Terminal application (Ctrl + Alt + T) or log into your server via SSH.
- To deeply scan the
/var/www/uploads/directory and return a list of every single file capable of being run as a program, type the following command exactly: find /var/www/uploads/ -type f -executable- Press Enter.
Permission Forensics
The -executable flag evaluates the exact permission matrix of the file relative to the user executing the find command. It checks if the file has the executable bit set (x) in the owner, group, or global permission blocks, and confirms that the current user has the authority to trigger it. We pair this command with -type f (regular files) because Linux inherently sets the execute bit on all directories to allow users to “cd” into them. This command is an absolute necessity for system administrators hunting for disguised payloads in unsecured upload directories.