# MacOS Apps - Inspecting, debugging and Fuzzing ## Static Analysis ### otool ```bash otool -L /bin/ls #List dynamically linked libraries otool -tv /bin/ps #Decompile application ``` ### SuspiciousPackage ****[**SuspiciousPackage**](https://mothersruin.com/software/SuspiciousPackage/get.html) 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: ```bash hdiutil attach ~/Downloads/Firefox\ 58.0.2.dmg ``` It will be mounted in `/Volumes` ### Objective-C When a function is called in a binary that uses objective-C, the compiled code instead of calling that function, it will call **`objc_msgSend`**. Which will be calling the final function: ![](<../../.gitbook/assets/image (560).png>) The params this function expects are: * The first parameter (**self**) is "a pointer that points to the **instance of the class that is to receive the message**". Or more simply put, it’s the object that the method is being invoked upon. If the method is a class method, this will be an instance of the class object (as a whole), whereas for an instance method, self will point to an instantiated instance of the class as an object. * The second parameter, (**op**), is "the selector of the method that handles the message". Again, more simply put, this is just the **name of the method.** * The remaining parameters are any** values that are required by the method** (op). | **Argument ** | **Register** | **(for) objc_msgSend** | | ----------------- | --------------------------------------------------------------- | ------------------------------------------------------ | | **1st argument ** | **rdi** | **self: object that the method is being invoked upon** | | **2nd argument ** | **rsi** | **op: name of the method** | | **3rd argument** | **rdx** | **1st argument to the method** | | **4th argument** | **rcx** | **2nd argument to the method** | | **5th argument** | **r8** | **3rd argument to the method** | | **6th argument** | **r9** | **4th argument to the method** | | **7th+ argument** |

rsp+
(on the stack)

| **5th+ argument to the method** | ### Packed binaries * Check for high entropy * Check the strings (is there is almost no understandable string, packed) * The UPX packer for MacOS generates a section called "\__XHDR" ## Dynamic Analysis {% hint style="warning" %} Note that in order to debug binaries, **SIP needs to be disabled **(`csrutil disable` or `csrutil enable --without debug`) or to copy the binaries to a temporary folder and **remove the signature **with `codesign --remove-signature `or allow the debugging of the binary (you can use [this script](https://gist.github.com/carlospolop/a66b8d72bb8f43913c4b5ae45672578b)) {% endhint %} {% hint style="warning" %} Note that in order to **instrument system binarie**s, (such as `cloudconfigurationd`) on macOS, **SIP must be disabled** (just removing the signature won't work). {% endhint %} ### dtruss ```bash 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** ```bash 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: ```bash 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](https://illumos.org/books/dtrace/chp-intro.html) #### Examples * In line ```bash #Count the number of syscalls of each running process sudo dtrace -n 'syscall:::entry {@[execname] = count()}' ``` * script ```bash syscall:::entry /pid == $1/ { } #Log every syscall of a PID sudo dtrace -s script.d 1234 ``` ```bash 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" ``` ```bash syscall:::entry { ; } syscall:::return { printf("=%d\n", arg1); } #Log sys calls with values sudo dtrace -s syscalls_info.d -c "cat /etc/hosts" ``` ### ProcessMonitor ****[**ProcessMonitor**](https://objective-see.com/products/utilities.html#ProcessMonitor) is a very useful tool to check the process related actions a process is performing (for example, monitor which new processes a process is creating). ### FileMonitor ****[**FileMonitor**](https://objective-see.com/products/utilities.html#FileMonitor) allows to monitor file events (such as creation, modifications, and deletions) providing detailed information about such events. ### fs_usage Allows to follow actions performed by processes: ```bash fs_usage -w -f filesys ls #This tracks filesystem actions of proccess names containing ls fs_usage -w -f network curl #This tracks network actions ``` ### TaskExplorer ****[**Taskexplorer**](https://objective-see.com/products/taskexplorer.html) is useful to see the **libraries** used by a binary, the **files** it's using and the **network** connections.\ It also checks the binary processes against **virustotal** and show information about the binary. ### lldb **lldb** is the de **facto tool **for **macOS** binary **debugging**. ```bash lldb ./malware.bin lldb -p 1122 lldb -n malware.bin lldb -n malware.bin --waitfor ``` | **(lldb) Command** | **Description** | | ----------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **run (r)** | Starting execution, which will continue unabated until a breakpoint is hit or the process terminates. | | **continue (c)** | Continue execution of the debugged process. | | **nexti (n)** | Execute the next instruction. This command will skip over function calls. | | **stepi (s)** | Execute the next instruction. Unlike the nexti command, this command will step into function calls. | | **finish (f)** | Execute the rest of the instructions in the current function (“frame”) return and halt. | | **control + c** | Pause execution. If the process has been run (r) or continued (c), this will cause the process to halt ...wherever it is currently executing. | | **breakpoint (b)** |

b main

b -[NSDictionary objectForKey:]

b 0x0000000100004bd9

br l #Breakpoint list

br e/dis <num> #Enable/Disable breakpoint

breakpoint delete <num>

| | **help** |

help breakpoint #Get help of breakpoint command

help memory write #Get help to write into the memory

| | **reg** |

reg read $rax

reg write $rip 0x100035cc0

| | **x/s \** | Display the memory as a null-terminated string. | | **x/i \** | Display the memory as assembly instruction. | | **x/b \** | Display the memory as byte. | | **print object (po)** |

This will print the object referenced by the param

po $raw

{

dnsChanger = {

"affiliate" = "";

"blacklist_dns" = ();

Note that most of Apple’s Objective-C APIs or methods return objects, and thus should be displayed via the “print object” (po) command. If po doesn't produce a meaningful output use x/b

| | **memory write** | memory write 0x100600000 -s 4 0x41414141 #Write AAAA in that address | {% hint style="info" %} When calling the **`objc_sendMsg`** function, the **rsi** register holds the **name of the method **as a null-terminated (“C”) string. To print the name via lldb do: `(lldb) x/s $rsi: 0x1000f1576: "startMiningWithPort:password:coreCount:slowMemory:currency:"` `(lldb) print (char*)$rsi:`\ `(char *) $1 = 0x00000001000f1576 "startMiningWithPort:password:coreCount:slowMemory:currency:"` `(lldb) reg read $rsi: rsi = 0x00000001000f1576 "startMiningWithPort:password:coreCount:slowMemory:currency:"` {% endhint %} ### Anti-Dynamic Analysis #### VM detection * The command **`sysctl hw.model`** returns "Mac" when the **host is a MacOS** but something different when it's a VM. * Playing with the values of **`hw.logicalcpu`** and **`hw.physicalcpu`** some malwares try to detect if it's a VM. * Some malwares can also **detect** if the machine is **VMware** based on the MAC address (00:50:56). * It's also possible to find **if a process is being debugged** with a simple code such us: * `if(P_TRACED == (info.kp_proc.p_flag & P_TRACED)){ //process being debugged }` * It can also invoke the **`ptrace`** system call with the **`PT_DENY_ATTACH`** flag. This **prevents** a deb**u**gger from attaching and tracing. * You can check if the **`sysctl` **or**`ptrace`** function is being **imported** (but the malware could import it dynamically) * As noted in this writeup, “[Defeating Anti-Debug Techniques: macOS ptrace variants](https://alexomara.com/blog/defeating-anti-debug-techniques-macos-ptrace-variants/)” :\ “_The message Process # exited with **status = 45 (0x0000002d)** is usually a tell-tale sign that the debug target is using **PT_DENY_ATTACH**_” ## Fuzzing ### [ReportCrash](https://ss64.com/osx/reportcrash.html#:\~:text=ReportCrash%20analyzes%20crashing%20processes%20and%20saves%20a%20crash%20report%20to%20disk.\&text=ReportCrash%20also%20records%20the%20identity,when%20a%20crash%20is%20detected.) ReportCrash **analyzes crashing processes and saves a crash report to disk**. A crash report contains information that can **help a developer diagnose** the cause of a crash.\ For applications and other processes** running in the per-user launchd context**, ReportCrash runs as a LaunchAgent and saves crash reports in the user's `~/Library/Logs/DiagnosticReports/`\ For daemons, other processes **running in the system launchd context** and other privileged processes, ReportCrash runs as a LaunchDaemon and saves crash reports in the system's `/Library/Logs/DiagnosticReports` If you are worried about crash reports **being sent to Apple** you can disable them. If not, crash reports can be useful to **figure out how a server crashed**. ```bash #To disable crash reporting: launchctl unload -w /System/Library/LaunchAgents/com.apple.ReportCrash.plist sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.ReportCrash.Root.plist #To re-enable crash reporting: launchctl load -w /System/Library/LaunchAgents/com.apple.ReportCrash.plist sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.ReportCrash.Root.plist ``` ### Sleep While fuzzing in a MacOS it's important to not allow the Mac to sleep: * systemsetup -setsleep Never * pmset, System Preferences * [KeepingYouAwake](https://github.com/newmarcel/KeepingYouAwake) #### SSH Disconnect If you are fuzzing via a SSH connection it's important to make sure the session isn't going to day. So change the sshd_config file with: * TCPKeepAlive Yes * ClientAliveInterval 0 * ClientAliveCountMax 0 ```bash sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist sudo launchctl load -w /System/Library/LaunchDaemons/ssh.plist ``` ### Internal Handlers [**Checkout this section**](./#file-extensions-apps)** **to find out how you can find which app is responsible of **handling the specified scheme or protocol**. ### Enumerating Network Processes This interesting to find processes that are managing network data: ```bash dtrace -n 'syscall::recv*:entry { printf("-> %s (pid=%d)", execname, pid); }' >> recv.log #wait some time sort -u recv.log > procs.txt cat procs.txt ``` Or use `netstat` or `lsof` ### More Fuzzing MacOS Info * [https://github.com/bnagy/slides/blob/master/OSXScale.pdf](https://github.com/bnagy/slides/blob/master/OSXScale.pdf) * [https://github.com/bnagy/francis/tree/master/exploitaben](https://github.com/bnagy/francis/tree/master/exploitaben) * [https://github.com/ant4g0nist/crashwrangler](https://github.com/ant4g0nist/crashwrangler) ## References * [**OS X Incident Response: Scripting and Analysis**](https://www.amazon.com/OS-Incident-Response-Scripting-Analysis-ebook/dp/B01FHOHHVS)**** * ****[**https://www.youtube.com/watch?v=T5xfL9tEg44**](https://www.youtube.com/watch?v=T5xfL9tEg44)**** * ****[**https://taomm.org/vol1/analysis.html**](https://taomm.org/vol1/analysis.html)****