Microsoft March 2025 XCSSET

Older XCSSET variants use `xxd` to encode modules. Later versions pass an `xxd` or `base64` encoded blob through multiple decoding stages to reconstruct the module name, AppleScript, or shell command. For example, the initial network request uses three layers of hex decoding before executing a curl command in a shell.

XCSSET installs malicious application bundles that mimic native macOS apps, such as Safari, by using the legitimate app’s icon and customizing the `Info.plist` to match expected metadata.

XCSSET retrieves files that match the pattern defined in the INAME_QUERY variable within the user's home directory, such as `*test.txt`, and are below a specific size limit. It then archives the files and exfiltrates the data over its C2 channel.

XCSSET has used `mdfind` to enumerate a list of apps known to grant screen sharing permissions and leverages a module to run the command `ls -la ~/Desktop`.

XCSSET's `dfhsebxzod` module searches for `.xcodeproj` directories within the user’s home folder and subdirectories. For each match, it locates the corresponding `project.pbxproj` file and embeds an encoded payload into a build rule, target configuration, or project setting. The payload is later executed during the build process.

Using AppleScript, XCSSET adds it's executable to the user's `~/.zshrc_aliases` file (`"echo " & payload & " > ~/zshrc_aliases"`), it then adds a line to the .zshrc file to source the `.zshrc_aliases` file (`[ -f $HOME/.zshrc_aliases ] && . $HOME/.zshrc_aliases`). Each time the user starts a new `zsh` terminal session, the `.zshrc` file executes the `.zshrc_aliases` file.

For several modules, XCSSET attempts to access or list the contents of user folders such as Desktop, Downloads, and Documents. If the folder does not exist or access is denied, it enters a loop where it resets the TCC database and retries access.

In older versions, XCSSET uses the plutil command to modify the LSUIElement, DFBundleDisplayName, and CFBundleIdentifier keys in the /Contents/Info.plist file to change how XCSSET is visible on the system. In later versions, XCSSET leverages a third-party notarized `dockutil` tool to modify the `.plist` file responsible for presenting applications to the user in the Dock and LaunchPad to point to a malicious application.