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defending against EvilOSX, a python RAT with a twist in its tail





Intro
EvilOSX is a malware project hosted on GitHub that offers attackers a highly customisable and extensible attack tool that will work on both past and present versions of macOS. The project can be downloaded by anyone and, should that person choose, be used to compromise the Macs of others.

What particularly interested me about this project was how the customisation afforded to the attacker (i.e., anyone who downloads and builds the project, then deploys it against someone else) makes it difficult for security software like my own DetectX Swift to accurately track it down when it’s installed on a victim’s machine.

In this post we’ll explore EvilOSX’s capabilities, customisations, and detection signatures. We’ll see that our ability to effectively detect EvilOSX will depend very much on the skill of the attacker and the determination of the defender.

For low-skilled attackers, we can predict a reasonably high success rate. However, attacker’s with more advanced programming skills that are able to customise EvilOSX’s source code to avoid detection are going to present a bigger problem. Specifically, they’re going to put defenders in an awkward position where they will have to balance successful detection rates against the risk of increasing false positives.

We’ll conclude the discussion by looking at ways that individuals can choose for themselves how to balance that particular scale.



What is it?
EvilOSX is best described as a RAT. The appropriately named acronym stands for remote access trojan, which in human language means a program that can be used to spy on a computer user by accessing things like the computer’s webcam, microphone, and screenshot utility, and by downloading personal files without the victim’s knowledge. It may or may not have the ability to acquire the user’s password, but in general it can be assumed that a RAT will have at least the same access to files on the machine as the login user that has been compromised.

Whether EvilOSX is intentionally malicious or ‘an educational tool’ is very much a matter of perspective. Genuine malware authors are primarily in the business of making money, and the fact that EvilOSX (the name is a bit of a giveaway) is there for anyone to use (or abuse) without obvious financial benefit to the author is arguably a strong argument for the latter. What isn’t in doubt, however, is that the software can be readily used for malicious purposes. Irresponsible to publish such code? Maybe. Malicious? Like all weapons, that depends on who’s wielding it. And as I intimated in the opening section, exactly how damaging this software can be will very much depend on the intentions and skills of the person ‘behind the wheel’.



How does it work?
When an attacker decides to use EvilOSX, they basically build a new executable on their own system from the downloaded project, and then find a way – through social engineering or exploiting some other vulnerability – to run that executable on the target’s system.

There is no ‘zero-day’ here, and out of the box EvilOSX doesn’t provide a dropper to infect a user’s machine. That means everybody already has a first line of defence against a malicious attacker with this tool: Prudent browsing and careful analysis of anything you download, especially in terms of investigating what a downloaded item installs when you run it (DetectX’s History function is specifically designed to help you with this).

EvilOSX doesn’t need to be run with elevated privileges, however, nor does the attacker need to compromise the user’s password. As intimated earlier, it’ll run with whatever privileges the current user has (but, alas, that is often Admin for many Mac users). All the attacker needs to do is to convince the victim to download something that looks innocuous and run it.

Once run, the malicious file will set up the malware’s persistence mechanism (by default, a user Launch Agent) and executable (the default is in the user’s ~/Library/Containers folder) and then delete itself, thus making it harder to discover after the fact how the infection occurred.

After successful installation, the attacker can now remotely connect to the infected machine whenever both the client (i.e., victim) and server (i.e., attacker) are online.







Once the attacker has surreptitiously connected to the client, there are a number of options, including webcam, screenshots, and downloading and exfiltrating browser history.







In my tests, some of the modules shown in the above image didn’t work, but the webcam, screenshots, browser history and the ability to download files from the victim’s machine were all fully functional.



Customisation options
By default, EvilOSX will offer the attacker the option of making a LaunchAgent with a custom name – literally, anything the attacker wants to invent, or to use the default com.apple.EvilOSX.







That in itself isn’t a problem for DetectX Swift, which examines all Launch Agents and their program arguments regardless of the actual filename. The malware also offers the option to not install a Launch Agent at all. Again, DetectX Swift will still look for the malware even if there’s no Launch Agent, but more on this in the final sections below.

If configured, the malware installs the Launch Agent and, by default, points it to run a binary located at ~/Library/Containers/.EvilOSX. There’s no option for changing this in the set up routine itself, but the path to the program argument is easily modified if the attacker is willing to do some basic editing of the source code.







Making matters even more difficult is that with a little know-how, the attacker could easily adapt EvilOSX to not use a Launch Agent at all and to use one of a variety of other persistence methods available on OSX like cron jobs, at jobs and one or two others that are not widely known. I’ll forego giving a complete rundown of them all here, but for those interested in learning more about it, try Jason Bradley’s OS X Incident Response: Scripting and Analysis for a good intro.



String pattern detection
Faced with unknown file names in unknown locations, how does an on-demand security tool like DetectX Swift go about ensuring this kind of threat doesn’t get past its detector search? Let’s start to answer that by looking at the attack code that runs on the victim’s machine.

We can see what the attack code is going to look like before it’s built from examining this part of the source code:







As the image above shows, the structure and contents of the file are determined by the output_file.write commands. Before exploring those, lets just take a look at what the finished file looks like. Here’s the start of the file:







and here’s the final lines:







Notice how the first four lines of the executable match up with the first four output_file.write commands. There’s a little leeway here for an attacker to make some customisations. The first line is required because, as noted by the developer, changing that will effectively nullify the ability of the Launch Agent to run the attack code. Line 4, or some version of it, is also pretty indispensable, as the malware is going to need functions from Python’s os module in order to run a lot of its own commands. Line 3, however, is more easily customised. Note in particular that the output_file.write instruction defines how long the random key shall be: between 10 and 69 (inclusive) characters long. One doesn’t have to be much of an expert to see how easy it would be to change those values.

Line 5 in the executable is where things get really interesting, both for attacker and defender. As it is, that line contains the entire attack code, encrypted into gibberish by first encoding the raw python code in base64 and then encrypting it with AES256. That will be random for each build, based on the random key written at Line 3. We can see this in the next image, which shows the encrypted code from three different builds. Everything from the highlighted box onwards to the last 100 or so characters of the script are random.







However, as one of my favourite 80s pop songs goes, some things change, some stay the same. The first thing that we can note, as defenders, is that when this code is running on a victim’s machine, we’re going to see it in the output of ps. If you want to try it on your own machine, run this from the command line (aka in the Terminal.app):

ps -axo ppid,pid,command | grep python | grep -v python

That will return anything running on your Mac with python in the command or command arguments.

Of course, the victim (and yourself!) may well have legitimate Python programs running. To limit our hits, we can run the file command on each result from ps and see what it returns. Our attack code, being a single, heavily encrypted and extremely long line in the region of 30,000 characters, will return this indicator:

file: Python script text executable, ASCII text, with very long lines

That still isn’t going to be unique, but the test will futher narrow down our list of candidates. We can then use string pattern detection on the remaining suspects to see which contain the following plain text items,

  • import os
  • exec("".join(os.popen("echo
  • -md sha256 | base64 --decode")
  • readlines()))
  • We could arguably even include this:

  • U2FsdGVkX1
  • which occurs immediately after echo, but for reasons I’m about to explain, that might not be a good idea. Still, from the default source code provided by the developer, if we find all of those indicators in the same file, we can be reasonably certain of a match (in truth, there’s a couple of other indicators that I haven’t mentioned here in order to keep DetectX Swift one-step ahead of the attackers).

    Unfortunately for defenders, the attacker has a few workarounds available to them for defeating string pattern detection. To begin with, the attacker could adapt the code to use something other than base64, or indeed nothing at all. Similary, AES256 isn’t the only option for encryption. For these reasons,we can’t assume that we’ll find something like U2FsdGVkX1 in the malicious file. Then, there’s the original source code’s use of the long-deprecated os.popen. That is an odd choice to start with, and someone with a bit of experience in Python would be able to rewrite that line to avoid the telling indicators.



    Skill level and customisation options




    Advanced detection options
    At this point you may be feeling that the attacker holds all the cards, and to a certain extent that is true, but there are some positive takeaways. First, we can be fairly sure of catching the neophyte hackers (aka “script kiddies”) with little to no programming experience who are trying to hack their friends, school or random strangers on the internet. The motivation to adapt the code is probably not going to be there for a large number of people just doing it 4 the lulz.

    Secondly, depending on your tolerance for investigating false positives, and as I’ll explain how below, if you needed to be super vigilant, you could simply check on every python executable running on your Mac which file identifies as having ‘very long lines’. For sure, there are legitimate programs doing that, but the number still isn’t going to be that high on any given machine, and the paths to those legit programs are going to be readily identifiable. If security is of overriding importance, then it’s not much inconvenience, and time well spent.

    By default, DetectX Swift will find instances of EvilOSX running on a mac when it’s used out of the box, and when its used with a modified launch agent and executable path. It will also still find it when the attacker has made certain alterations to the source code. However, a determined attacker who chooses to rewrite the source code specifically to avoid string pattern detection is always going to be one-step ahead of our heuristics.

    We are not out of options though. You can still use DetectX Swift combined with the Terminal.app as a means to making custom detections as mentioned above. Here’s how:

    1. Launch DetectX Swift and allow it to search for the variations of EvilOSX it knows about. If nothing is returned, go into the Profile view.
    2. Click inside the dynamic profiler view, and press Command-F and type python into the search field.
    3. If there are no hits in the Running Processes section, you don’t have EvilOSX running on your machine.
    4. If there are any hits within the Running Processes section, make a note of each one’s command file path by selecting it in the view and pressing Command-C to copy it.
    5. Switch to the Terminal app, type file (with a space) and Command-V to paste. If the path has any spaces in it, surround it in single quotes. Then press return.
    6. If the path doesn’t come back with ‘very long lines’, the file isn’t EvilOSX.
    7. If it does, hit the up arrow on the keyboard to put the previous command back at the prompt, use Control-A to move the cursor to the beginning of the line, and replace the word file with cat (if you’re familiar with Vi or similar command line text editors use one of those instead). Hit return.
    8. Inspect the output from cat with the following in mind:

    9. Does the file end with readlines()))?
    10. Use command and the up arrow to go back up to the beginning of the file. How close does the file look to matching what you’ve seen here? Look for variations like import * from os and import subprocess.
    11. Consider the path that you pasted in. Is it something that looks like it belongs to a genuine program, or is it a completely unfamiliar? Anything that points to ~/Library and isn’t contained within a recognized application named folder should warrant further investigation.

    You’ll need to consider carefully the answers to 8, 9, & 10, with an emphasis on the latter, for each python file you tested to make an assessment. If you’re in any doubt, contact us here at Sqwarq and we’ll be glad to take a look at it and confirm one way or the other.



    Conclusion
    EvilOSX is just one of an increasing number of Python RAT projects that are appearing on the internet. It’s not particularly sophisticated, and this is both a strength and a weakness. With modest programming skills, an attacker can modify the source code to increase the chances of evading automated detections. However, vigilant users can still identify EvilOSX if they know what to look for, as explained in the preceding sections of this post, or by contacting Sqwarq support for free advice.

    Stay safe, folks! 🙂


    how to remove MyCouponize adware





    MyCouponize is an aggressive adware infection that simultaneously installs itself in Safari, Chrome and Firefox, It hijacks the user’s search and page loads, redirecting them to multiple web sites that advertise scamware and other unwanted junk.

    You can remove it easily with DetectX Swift (a free/shareware utility written by myself) as shown in this video. If you prefer reading to watching, here’s the procedure:

    1. Run the search in DetectX.







    2. Click on the [X] button.
    You’ll find this button just above the results table to the right, between the search count and the tick (whitelist) button. It will turn red when you hover over it. When it does so, click it.
    Then hit ‘Delete’ to remove all the associated items.
    You’ll need to enter a password as some of the items are outside of your user folder.
    Press the esc key or click the ‘Cancel’ button on any pop up dialogs that appear.

    3. Go to the Profiler
    Here we’ll unload the launchd processes that belong to MyCouponize.

    Navigate to the user launchd processes section and move the cursor over the item com.MyMacUpdater.agent







    Click the ‘Remove x’ button that appears when the line is highlighted.
    Wait for the profiler to refresh and then go back to the same section and remove the second process called com.MyCouponize.agent

    4. Quit the mediaDownloader.app
    This item has already been deleted in step 1, but its process may still be running in memory. If its icon appears in the Dock, right click on it and choose ‘Quit’ from the menu.







    4. Finally, go to Safari Preferences’ Extensions tab
    Click the uninstall button to remove the MyCouponize extension.







    After that, Safari should be in good working order. If you have Chrome, Firefox or possibly other browsers installed, make sure you remove the extensions or Add Ons from those, too.

    DetectX and DetectX Swift are shareware and can be used without payment, so go grab yourself a copy over at sqwarq.com.


    yes, enable the root user if you’re on High Sierra

     

    Update: There’s a security update available in the App Store now that mitigates this risk. It should be applied by all High Sierra users as a matter of urgency.



    Today has been all about a monumental security flaw in High Sierra which allows anyone to log in to a mac and immediately become the root user without a password at all.

    If you haven’t yet seen the news, check out the 30-second video above. If you’re not on High Sierra, no need to worry.

    Although there are conflicting reports of exactly under what conditions the exploit can be triggered, it seems that in most cases two attempts are required to escalate user privileges. The first time enables the root user with the password that you do or do not put in the password field (i.e., it’ll accept a blank password). The second time is using those credentials to unlock whatever it is you want to unlock (in the video, only 1 attempt is shown as I had already ran the exploit once prior to making the video). There also seems to be conflicting reports about whether the flaw can be exploited remotely. What does seem certain is that malicious 3rd party applications could programmatically use it to escalate privileges for themselves, so it’s important to make sure you take the proper precautions to deal with this flaw until Apple patches it with an update.

    Alas, with so much excitement, it seems some people are getting confused about exactly what needs to be done to avoid falling victim to this security flaw. The answer is not, as has been mistakenly suggested in some quarters, to disable the root user, but quite the reverse: you need to enable it.

    The one thing that stops the flaw from being exploited is having the root user already enabled and set with a strong password.

    By default, macOS ships with the root user disabled, so unless you (or someone who administrates your mac) has enabled it at some point, it won’t be set. If you’re not sure, this AppleScript will quickly tell you the status of the root user:

     

    Update: further testing on 10.13 shows that the root user may be enabled without writing a ShadowHash entry to dscl. In that case, the script would incorrectly indicate root was disabled. Thus, to be certain, the best way to check is to follow the instructions in the apple support article linked to below.

    If you find the root user is disabled, then go and enable it by following Apple’s instructions here:

    https://support.apple.com/en-us/HT204012

    Be sure to use a strong password of at least 14 characters or more. You can save the password if you want, but it doesn’t really matter much if you forget it. There’s really never any need for an admin user to require the root user at all, and there are other ways to get root privileges safely through the Terminal if needs be.

    how to easily spoof a user’s password





    Spoofing or phishing – presenting a user with fake authentication requests – is a common email tactic, but it’s not the only vector where you need to be on your guard. Every version of macOS is vulnerable to a very simple phishing attack right on your desktop that doesn’t require admin privileges to run, would not be detected by GateKeeper or XProtect, and which could easily be placed on your mac by any of the nefarious malware / adware installer scripts that come with some less reputable software downloads.

    This attack isn’t new, but it’s not often talked about. The easiest way to see how it works is in this quick 4-minute demo:

    As you can see, it’s easy to grab the icon of any Application and put it in the script; it doesn’t even have to be the icon of an app that’s running. The simple demo I gave above could easily launch iTunes first to increase the coherence of the attack, or it could use a completely different icon, including the icon of security programs you may have running on your mac.

    How can you check?

    If you were presented with a password request like this and wanted to check whether it’s legitimate or not, an easy way would be to use my free utility DetectX Swift’s Profiler. Click the Profiler function, and search for ‘osascript’ within the Running Processes section. Note how DetectX Swift shows you the text of the script being run, confirming that this dialog is up to no good:


    DetectX Swift History

    DetectX Swift beta has arrived

    It’s been unusually quiet on Applehelpwriter these past few months, and the reason is that I’ve been devoting all my time and efforts to the new version of DetectX. The new version is called DetectX Swift because (yeah, you guessed it) I wrote it in Swift and because it’s considerably faster than its older sibling.

    DetectX Swift’s got a new interface, but there’s far more going on under the hood. The Search uses some fancy heuristics as well as hard-coded and live update search definitions to ensure it provides the very best in security threat scanning.

    The new Profile view employs some super cool dynamic highlighting and lets you inspect the contents not only of directories but also of scripts, plists and other files that could execute troublesome code on your mac.

    There’s changes in the History view, too, both in the display and functions. One of the coolest things I like about the new History function is that you can run a diff on any previous run against the latest run, immediately seeing how they differ.

    There’s tons more to DetectX Swift, but the best way to find out about it is just to try it. The beta version is free to use for both Home and Commercial users, so just head off over to its home page and grab yourself a copy!

    Don’t forget to keep us informed of how it goes. The beta is still in an early stage and more features are slated as it develops, but feel free to tell us about anything that you feel could be done better or things that you’d like to see added.

    Share and enjoy! 🙂

    getting ready for DetectX Swift

    Screen Shot 2017-10-04 at 16.18.14

    Pretty soon now I’ll be releasing the first beta of DetectX Swift. Lots more details will be forthcoming over the next few days and weeks, but here’s a quick 1-minute look at how the new Profiler function works and some of the cool things you can do with it.

     

    how to retrieve forgotten Wifi password


    At our house, giving visitors the wifi password is always an exercise in frustration. Can’t remember? Oh, then I’ve got to either go trawling through Keychain Access or log in to the router, neither of which are particularly appealing.

    Here’s an easier way. It’ll require an admin password (and you’ll need to supply it for as many passwords as you’re looking for – no ‘with administrator privileges’ will help here I’m afraid), but otherwise requires nothing more than a quick double-click of this saved script, once you’ve added your own SSID names in place of the dummy ones.

    Just to be clear, you do NOT need to add the passwords to the script. So long as the mac that you run this script on already knows the Wifi password, the script will retrieve it.

    Get the script from my pastebin

    Enjoy!

    how to create a bootable macOS installer

    If you are preparing to install macOS on multiple computers, one of the things that can make your life simpler (and the waiting shorter) is a bootable USB installer.

    The idea of the installer is that you only need to download the macOS Installer.app from the App Store once. Usually, when you run the installer after downloading it, it’ll delete itself and you have to go through the whole download process again on each machine or disk that you want to install macOS onto. By making a bootable USB drive, you simply plug the drive in to your mac, launch the installer app and tell it where to install the OS. You can repeat this as many times as you like as the installer will remain safe on your USB.

    There are various ways to make a bootable USB installer, but they all involve the same process:

    1. Download the macOS Installer from the App Store.
    2. Run the createinstallmedia command from the Terminal, an AppleScript or a helper app.
    3. Reboot your mac, choosing the newly created USB as the startup disk.
    4. Run the installer.app from the USB.

    Step 2 is where the fun is. The createinstallmedia command can be tricky to get right, particularly if you’re not familiar with working on the command line. For those of you that are, follow Apple’s instructions here.

    For a little more convenience, I wrapped all that inside an AppleScript which will first ask you for the location of the installer, then ask you to choose the USB target.

    For maximum convenience, I also wrote a free little Swift app I’ve dubbed ‘Boot Buddy‘ (cos “Create bootable macOS Installer Drive.app” just didn’t quite have the right ring to it..!) that will present the whole thing in a neat little user interface. Three clicks, more or less, and you’re done.

    Boot Buddy doesn’t require an admin password to install, but you do need to provide an admin password to actually create the bootable installer as the createinstallmedia process has to be run as root. Boot Buddy doesn’t see or use this in any way whatsoever other than to start the createinstallmedia process or to cancel it (if you choose to do so); authorisation is handed off to macOS to take care of.

    Boot Buddy requires macOS 10.11 or higher and can create bootable USBs from Mavericks, Yosemite, El Capitan, Sierra and High Sierra installer apps.











    Share and enjoy! 🙂


    how to reveal hidden users


    With malware big in the news again, and evidence that at least one malware variant that targets macOS creates hidden users on the victim’s system, here’s a timely tip on how to check for unwelcome guests.

    For this tip, we’re going to use the Terminal, which you can find in the /Applications/Utilities folder. If you’re not a frequent visitor to the land of the command line, you might want to see my 3-part series “Learning the Terminal”.

    Regardless, the first thing we’re going to do in Terminal is about the simplest command you’ll ever type: w. Yep, type a single ‘w’ at the prompt and press return.





    The w utility is a very quick way to see who’s currently logged on to your system and to ensure that there’s no surprises. You should see a couple of entries for yourself: one as ‘console’ and one as ‘s***’. The first represents a login through the usual Desktop GUI login window; the second is there because you just logged into Terminal. Anybody else logged in either via the command line (like a potential remote user) or the GUI will show up here. Notice that on my machine, there’s another user called ‘Developer’ who hasn’t logged in using the GUI, but is logged in via a command line interface. Note that ‘w’ returns the full user name, not the short one.

    While the w utility will tell you if a hidden user is currently logged on, what if there’s a hidden user that isn’t active at the particular time you check? To look for those, we have a couple of options. First, we can use the dscl utility to list all users, and you might be surprised at how many there are:

    dscl . -list /Users

    Look to the end of that list where the names that don’t begin with an underscore start. ‘Daemon’, ‘Nobody’, ‘Root’ and ‘Guest’ are all standard system accounts, as are all those entries that begin with an underscore. Don’t worry about those. However, aside from those, you should only see names that you recognise. To make things a little easier, we can add another command to the dscl command to filter that list. Try this

    dscl . -list /Users | grep -vE ‘_|root|nobody|daemon|Guest’

    That should now only return the names of real users. There shouldn’t be any names in there you don’t recognise. In my example, I know the last three, but the first one ‘dev’ isn’t familiar to me. Note that unlike ‘w’, this command returns short user names, and that ‘dev’ looks very much like it’s the same account as ‘Developer’ that I saw earlier.




    However, what we have so far is a list of users, not a list of hidden users. To see specifically if any accounts are hidden, we need a longer command:

    defaults read /Library/Preferences/com.apple.loginwindow

    Normally, when there are no hidden users, this will return the contents of a property list file that may look something like this:

    {
    GuestEnabled = 1;
    OptimizerLastRunForBuild = 31898816;
    OptimizerLastRunForSystem = 168494592;
    SHOWFULLNAME = 1;
    lastUser = loggedIn;
    lastUserName = imackim;
    }




    That tells us that there’s no hidden users on this mac. How so? Because if there were it would return something very different, like this:





    We can see not only the list of hidden users, but also that the preference for hiding users has been set to ‘1’ (in plist syntax, ‘1’ means true and ‘0’ means false). Note again that unlike the dscl command above, this returns the account’s full name, not the short user name.

    If we’d like to ‘unhide’ that user, so the account appears in the login window GUI and in System Preferences’ ‘Users & Groups’ pane, we’ll need admin privileges. To do that, cut and paste the following into Terminal:

    sudo defaults write /Library/Preferences/com.apple.loginwindow Hide500Users -bool NO

    Supply an admin user password at the prompt and hit ‘return’, but type slowly as the display doesn’t register your key presses, which makes it easy to fat finger your password.

    Next, we need to change the IsHidden key in dscl for that user, so

    sudo dscl . -change /Users/dev IsHidden 1 0

    In the above command, substitute my user’s shortname dev for the shortname of the user on your machine. The 1 0 is the old value (hidden) followed by the new value (unhidden). The line can be read as “change User dev’s IsHidden value from hidden to unhidden.”



    For the more advanced
    We can save ourselves some typing by putting much of this into a script so that we can run it whenever we want. If you’re not familiar with how to create and use bash scripts, take a look here.

    Our script will basically do the same as all the commands we listed above (except changing the prefs for Hide500Users) in one fell swoop, and there’s a couple of little twists that I’ll leave as an exercise for the reader to figure out. To save on the typing, you can copy the whole script from my pastebin here.



    The script’s output is illustrated in the shot at the top of this post.

    Enjoy! 🙂

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