Detect attempts by potentially malicious software to discover the presence of Little Snitch on a host by looking for process and command line artifacts.

• Unix Ps Grep
• Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Line
• Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Line
• Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep List
• Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Free

These attempts are categorized as Discovery / Security Software Discovery.

The strategy will function as follows:

• Record process and process command line information for MacOS hosts using endpoint detection tooling.
• Look for any explicit process or command line references to Little Snitch.
• Suppress known-good processes and command line arguments
  • Little Snitch Updater
  • Little Snitch Installer
  • Health checks for Little Snitch
• Fire alert on any other process or command line activity.

Little Snitch is an application firewall for MacOS that allows users to generate rulesets around how applications can communicate on the network.

$ grep Manager employee.txt grep Sales 100 Thomas Manager Sales $5,000 500 Randy Manager Sales $6,000 Grep NOT 7. Grep NOT using grep -v. Using grep -v you can simulate the NOT conditions.v option is for invert match. I.e It matches all the lines except the given pattern. Grep -v 'pattern1' filename. Grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.L, -files-without-match Suppress normal output; instead print the name.

Unix Ps Grep

In the most paranoid mode, Little Snitch will launch a pop-up notifying the user that an application has deviated from a ruleset. For instance, the following events could trip an interactive alert:

A new process is observed attempting to communicate on the network.A process is communicating with a new IP address or port which differs from a ruleset.The following prompt demonstrates the expected behavior of Little Snitch:

Due to the intrusive nature of Little Snitch popups, several MacOS implants will perform explicit checks for processes, kexts, and other components. This usually manifests through explicit calls to the process (ps) or directory (dir) commands with sub-filtering for Little Snitch.

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For instance, an implant could look for the following components:

• Running Little Snitch processes
• Little Snitch Kexts
• Little Snitch Plists
• Little Snitch Rules

The following code is explicitly run by the Powershell Empyre agent as soon as it executes on a MacOS system:

The following screenshot shows the same command as part of a endpoint detection tooling process execution chain:

Looking at the source code for Powershell Empyre reveals the explicit check using the ps and grep commands:

This strategy relies on the following assumptions:

• Endpoint detection tooling is running and functioning correctly on the system.
• Process execution events are being recorded.
• Logs from endpoint detection tooling are reported to the server.
• Endpoint detection tooling is correctly forwarding logs to SIEM.
• SIEM is successfully indexing endpoint detection tooling logs.
• Attacker toolkits will perform searches to identify if Little Snitch is installed or running.

A blind spot will occur if any of the assumptions are violated. For instance, the following would not trip the alert:

• Endpoint detection tooling is tampered with or disabled.
• The attacker implant does not perform searches for Little Snitch in a manner that generates a child process.
• Obfuscation occurs in the search for Little Snitch which defeats our regex.

There are several instances where false positives for this ADS could occur:

• Users explicitly performing interrogation of the Little Snitch installation
  • Grepping for a process, searching for files.
• Little Snitch performing an update, installation, or uninstallation.
  • We miss whitelisting a known-good process.
• Management tools performing actions on Little Snitch.
  • We miss whitelisting a known-good process.

Known false positives include:

• Little Snitch Software Updater

Most false positives can be attributed to scripts or user behavior looking at the current state of Little Snitch. These are either trusted binaries (e.g. our management tools) or are definitively benign user behavior (e.g. the processes performing interrogation are child processes of a user shell process).

The priority is set to medium under all conditions.

Validation can occur for this ADS by performing the following execution on a MacOS host:

In the event that this alert fires, the following response procedures are recommended:

• Look at management tooling to identify if Little Snitch is installed on the host.
  • If Little Snitch is not installed on the Host, this may be more suspicious.
• Look at the process that triggered this alert. Walk the process chain.
  • What process triggered this alert?
  • What was the user the process ran as?
  • What was the parent process?
  • Are there any unusual discrepancies in this chain?
• Look at the process that triggered this alert. Inspect the binary.
  • Is this a shell process?
  • Is the process digitally signed?
  • Is the parent process digitally signed?
  • How prevalent is this binary?
• Does this appear to be user-generated in nature?
  • Is this running in a long-running shell?
  • Are there other indicators this was manually typed by a user?
  • If the activity may have been user-generated, reach out to the user via our chat client and ask them to clarify their behavior.
• If the user is unaware of this behavior, escalate to a security incident.
• If the process behavior seems unusual, or if Little Snitch is not installed, escalate to a security incident.

I use ps command to find out all running process on my Linux and Unix system. The ps command shows information about a selection of the active processes on shell. You may also pipe out ps command output through grep command to pick up desired output.

Example: Remove grep command while grepping using ps

Let us run a combination of ps command and grep command to find out all Perl processes:
$ ps aux grep perl
Sample output:

In above example, I am getting the grep process itself. To ignore grep process from the output, type any one of the following command at the CLI:
$ ps aux grep '[p]erl'
OR
$ ps aux grep perl grep -v grep
Sample outputs:

The above output indicate that I prevented ‘grep’ from showing up in ps results. In other words, we learned to remove grep command from ps output.

Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Line

Understanding above commands

You don’t want display grep command as the process in ps output, i.e., you want to prevent ‘grep’ from showing up in ps results.

• In first command I used regex. It says find the character ‘p’ followed by ‘erl’ i.e. the expression ‘[p]erl’ matches only ‘perl’ not ‘[p]erl’, which is how the grep command itself is now shown in the process list.
• The second command uses the -v option to invert the sense of matching, to select non-matching lines.

Say hello to pgrep

You can look up process based upon name to get PID. This is only useful when looking for process names and PIDs The syntax is:
pgrep process-name
pgrep -a process
pgrep -l process
pgrep -u user -a process
To find the process ID of the sshd daemon:
$ pgrep -u root sshd
1101
To list PID and full command line pass the -a to the pgrep command:
$ pgrep -a sshd
Sample outputs:

To just list PID and process name pass the -l to the pgrep command:
$ pgrep -l firefox
7981 firefox

Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Line

Conclusion

Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep List

You learned how to avoid grep command from showing up in ps command results under Linux, macOS, *BSD or Unix-like systems. Pretty useful for excluding grep from process list when running ps. For more information see ps and grep command man pages by typing the following commands:
man ps
man grep

Import Re Subprocess Cmd Ps Grep Little Snitch Grep Grep Free

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