Masquerading: Space after Filename

Adversaries can hide a program's true filetype by changing the extension of a file. With certain file types (specifically this does not work with .app extensions), appending a space to the end of a filename will change how the file is processed by the operating system.

For example, if there is a Mach-O executable file called evil.bin, when it is double clicked by a user, it will launch and execute. If this file is renamed to evil.txt, then when double clicked by a user, it will launch with the default text editing application (not executing the binary). However, if the file is renamed to evil.txt (note the space at the end), then when double clicked by a user, the true file type is determined by the OS and handled appropriately and the binary will be executed [1].

Adversaries can use this feature to trick users into double clicking benign-looking files of any format and ultimately executing something malicious.

ID: T1036.006
Sub-technique of:  T1036
Tactic: Defense Evasion
Platforms: Linux, macOS
Permissions Required: User
Contributors: Erye Hernandez, Palo Alto Networks
Version: 1.0
Created: 10 February 2020
Last Modified: 29 March 2020

Procedure Examples

ID Name Description
S0276 Keydnap

Keydnap puts a space after a false .jpg extension so that execution actually goes through the program.[2]


This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.


ID Data Source Data Component
DS0022 File File Metadata

It's not common for spaces to be at the end of filenames, so this is something that can easily be checked with file monitoring. From the user's perspective though, this is very hard to notice from within the or on the command-line in Processes executed from binaries containing non-standard extensions in the filename are suspicious.