Query: detect Hidden Files and Directories
Matching passage: T1564.001 Hidden Files and Directories. Tactics: stealth. Description: Adversaries may set files and directories to be hidden to evade detection mechanisms. To prevent normal users from accidentally changing special files on a system, most operating systems have the concept of a ‘hidden’ file. These files don’t show up when a user browses the file system with a GUI or when using normal commands on the command line. Users must explicitly ask to show the hidden files either via a series of Graphical User Interface (GUI) prompts or with command line switches (<code>dir /a</code> for Windows and <code>ls –a</code> for Linux and macOS). On Linux and Mac, users can mark specific files as hidden simply by putting a “.” as the first character in the file or folder name (Citation: Sofacy Komplex Trojan) (Citation: Antiquated Mac Malware). Files and folders that start with a period, ‘.’, are by default hidden from being viewed in the Finder application and standard command-line utilities like “ls”. Users must specifically change settings to have these files viewable. Files on macOS can also be marked with the UF_HIDDEN flag which prevents them from being seen in Finder.app, but still allows them to be seen in Terminal.app (Citation: WireLurker). On Windows, users can mark specific files as hidden by using the attrib.exe binary. Many applications create these hidden files and folders to store information so that it doesn’t clutter up the user’s workspace. For example, SSH utilities create a .ssh folder that’s hidden and contains the user’s known hosts and keys. Additionally, adversaries may name files in a manner that would allow the file to be hidden such as naming a file only a “space” character. Adversaries can use this to their advantage to hide files and folders anywhere on the system and evading a typical user or system analysis that does not incorporate investigation of hidden files.
Near-miss passage: T1564.013 Bind Mounts. Tactics: stealth. Description: Adversaries may abuse bind mounts on file structures to hide their activity and artifacts from native utilities. A bind mount maps a directory or file from one location on the filesystem to another, similar to a shortcut on Windows. It’s commonly used to provide access to specific files or directories across different environments, such as inside containers or chroot environments, and requires sudo access. Adversaries may use bind mounts to map either an empty directory or a benign `/proc` directory to a malicious process’s `/proc` directory. Using the commands `mount –o bind /proc/benign-process /proc/malicious-process` (or `mount –B`), the malicious process's `/proc` directory is overlayed with the contents of a benign process's `/proc` directory. When system utilities query process activity, such as `ps` and `top`, the kernel follows the bind mount and presents the benign directory’s contents instead of the malicious process's actual `/proc` directory. As a result, these utilities display information that appears to come from the benign process, effectively hiding the malicious process's metadata, executable, or other artifacts from detection.(Citation: Cado Security Commando Cat 2024)(Citation: Ahn Lab CoinMiner 2023)