Inspecting and debugging Mac OS Sotware

Static Analysis

otool

otool -L /bin/ls #List dynamically linked libraries
otool -tv /bin/ps #Decompile application

SuspiciousPackage

****SuspiciousPackage is a tool useful to inspect .pkg files installers and see what is inside before installing it.
These installers have preinstall and postinstall bash scripts that malware authors usually abuse to persist the malware.

hdiutil

This tool allows to mount Apple disk images **.dmg** files to inspect them before running anything:

hdiutil attach ~/Downloads/Firefox\ 58.0.2.dmg

It will be mounted in /Volumes

Dynamic Analysis

{% hint style="warning" %} These tools require SIP to be disabled or to copy the binaries to a temporary folder and remove the signature with codesign --remove-signature <binary-path> {% endhint %}

dtruss

dtruss -c ls #Get syscalls of ls
dtruss -c -p 1000 #get syscalls of PID 1000

ktrace

You can use this one even with SIP activated

ktrace trace -s -S -t c -c ls | grep "ls("

dtrace

It allows users access to applications at an extremely low level and provides a way for users to trace programs and even change their execution flow. Dtrace uses probes which are placed throughout the kernel and are at locations such as the beginning and end of system calls.

The available probes of dtrace can be obtained with:

dtrace -l | head
   ID   PROVIDER            MODULE                          FUNCTION NAME
    1     dtrace                                                     BEGIN
    2     dtrace                                                     END
    3     dtrace                                                     ERROR
   43    profile                                                     profile-97
   44    profile                                                     profile-199

The probe name consists of four parts: the provider, module, function, and name `fbt:mach_kernel:ptrace:entry`. If you not specifies some part of the name, Dtrace will apply that part as a wildcard.

A more detailed explanation and more examples can be found in https://illumos.org/books/dtrace/chp-intro.html

Examples

In line

#Count the number of syscalls of each running process
sudo dtrace -n 'syscall:::entry {@[execname] = count()}'

script

syscall:::entry
/pid == $1/
{
}

#Log every syscall of a PID
sudo dtrace -s script.d 1234

syscall::open:entry
{
    printf("%s(%s)", probefunc, copyinstr(arg0));
}
syscall::close:entry
{
        printf("%s(%d)\n", probefunc, arg0);
}

#Log files opened and closed by a process
sudo dtrace -s b.d -c "cat /etc/hosts"

syscall:::entry
{
        ;
}
syscall:::return
{
        printf("=%d\n", arg1);
}

#Log sys calls with values
sudo dtrace -s syscalls_info.d -c "cat /etc/hosts"

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