What Is The New Steganographic Campaign Distributing Multiple Malware
Recently we have observed multiple stealer malware such as Remcos, DcRAT,AgentTesla, VIPKeyLogger, etc. distributed through a steganographic campaign. On tracing the roots, the campaign has been around for a while but has not been active since long. What makes the campaign interesting is the way the attack is orchestrated.
In this blog, we will discuss distribution of Remcos and AsyncRAT via the campaign observed by us.
Infection- Chain:
The infection-chain starts with a phishing mail containing an excel file which exploits a vulnerability in excel and issues an http request to download a .hta file. The .hta file consisting of .vbs code writes a batch file which connects to a paste URL and downloads another obfuscated .vbs script. The .vbs script downloads a .jpg file containing padded base64 encoded second stage payload (malicious loader) file, which is decoded, and a function VAI is invoked through script. The loader file which gets a URL and targeted process name as argument, downloads a reversed base64 encoded file which when decoded gives us the final payload.
Phishing Email: The initial point of attack is a phishing email, containing a malicious excel document which masquerades itself as a genuine file tricking users to open the attachment which contains the malicious code.
Excel document containing malicious ole package:
The file is an exploit which leverages vulnerability CVE-2017-0199. It contains an embedded OLE2 embedded link object which issues an http request when we open the file.
.HTA Script
.hta file contains vbs code (Fig.4) that writes batch file which connects to a paste URL and downloads a vbs file which is a script with a huge chunk of garbage code (Fig.5).
The script writes VBS Script2:
On removal of the junk code and simplification, we get a base-64 encoded script which will be run using PowerShell (Fig.6).
Take note, here while VAI method is being invoked, url is being passed in first argument which is stored in $deject variable and the fifth argument is also important which we will discuss later while discussing our second payload which is injector dll.
In a similar way we found AsyncRAT being distributed, mostly the initial chain will be the same, but we weren’t able to trace it back. In AsyncRAT’s case, the vbs script is masquerading as prnmngr.vbs tricking the user into thinking of it as a genuine script which adds, removes, and lists printers or printer connections, in addition to setting and displaying the default printer. But there is a small chunk of malicious code inserted in between to escape suspicion.
Below is the chunk of code, which downloaded the JPG image from the hard coded URL [hxxps://watchonlinehotvideos[.]top/omfg[.]jpg] similar as explained in the previous case
Same as we took a note for previous script, here the first argument passed is our reversed URL in variable $restoredtext and looks like a gibberish value/ random string being passed in other arguments and again we will keep fifth argument in mind.
In both cases the sample is using steganography, the jpg file (Fig11.) downloaded conceals itself as a harmless picture which contains base64 encoded malware. As you can see in Fig7., it checks the marker <<BASE64 START>> and <<BASE64 END>> to get the whole malicious file and that is then decoded.
Both the files are VB.NET dll file with internal filename as “Microsoft.Win32.TaskScheduler.dll” maybe to trick users in thinking it as a Microsoft dll.
Both DLLs are obfuscated but on different levels. The one that that we got from Remcos campaign even has some common .NET function name obfuscated but in other case some of it were straight. But the code of the DLL was the same, doing the same thing.
The DLL code is obfuscated but we can see the arguments being passed to it. Threat actor invoked the VAI method with 15 arguments. Based on passed argument the method will have capabilities such as loading another malware executable by process hollowing, creating persistence, etc.
The first argument passed in the script (Fig7. /Fig10.) while invoking the method is our URL stored in variable $deject/$restoredtext is passed here as QBXtX.
The value persistencia is null/gibberish value and the other value, which is passed decodes to 1, this is passed to Delegate11.smethod_0 and it returns boolean value. So, the final value will be 0 and the condition will fail. Hence, there will be no activity to remain persistent.
The reversed URL, which is passed in argument QBXtX is stored in “text5” is reversed and with help of web client it downloads the data in “text6” string which is base64 encoded data in reverse format (Fig14). This is our final payload which alongwith the path “C:WindowsSysWOW64” (decoded from Class219.smethod(10577)) of “caspol.exe” / “msbuild.exe” (fifth arguments) is passed as an argument to the “Tools.Ande” function. This function does the process hollowing with the targeted process which is being supplied as fifth argument (Fig15).
As shown above, a new process is created using CreateProcess API in suspended state. The newly created process is unmapped using NtUnmapViewOfSection and memory is allocated using VirtualAllocEx, where the malicious code is then injected. With the use of SetThreadContext it adds the entry point to the injected code and finally, the process is resumed with ResumeThread.
In our case, the final payload that we got is a Remcos and AsyncRAT Sample (Fig16).
Final Payload: Remcos
Remcos has always been around the malware world since its inception in 2016. From version as early as 1.0 to the most recent one, what keeps Remcos still relevant is in handling its core capability of command and control. Starting as a closed-source tool that was marketed as remote control and surveillance software, Remcos has come along a long way.
Remcos mostly have a setting block with a batch of configurations which is encrypted and saved in the Resource section named “SETTINGS,”. It gets decrypted at the start and initializes Remcos with the setting block.
Remcos connects to C2 for C&C communication and further awaits the commands sent by the attacker. The key details from the configuration data extracted is as follows:
C2: interestedthingsforkissinggirlwithloves[.]duckdns[.]org
Filename: Remcos.exe
Botnet name: zyno007
Mutex Created: Rmc-IB3RDF
Further, in some cases Remcos is seen deploying malware like AgentTesla too.
Final Payload: AsyncRAT
AsyncRAT is a remote access Trojan (RAT), written in C# which offers standard RAT and information-stealing features, including the capabilities of logging keystrokes, execution/injection of additional payload, command-and-control, etc.
The backdoor has capabilities based upon the embedded configuration. As you can see in the figure below (Fig19.), the execution starts with a De_lay function which defines sleep duration, mostly done to evade sandboxes.
The InitializeSettings() function here accesses all the hardcoded configuration which is AES encrypted.
The verifyhash() function (Fig20.) in last checks if the configurations are valid or not using the server certificate and server signature. The key details from the configuration data extracted are as follows:
Ports:7878
Hosts:148[.]113[.]214[.]176
Version:1.0.7
MTX: asasasas2242dqwe
Pastebin: null
Group:Diama
The Pastebin value is used by “WebClient.DownloadString” API (Fig21.) which can download additional resources and other payloads from Pastebin or other domains. In our case, it is null, so it selects hosts and port from the configuration and employs socket connection to interact with C2.
IOCS:
| Remcos IOC’s |
| 9d66405aebff0080cc5d28a1684d501fa7e183dc8b6340475fc06845509cb466 |
| 42813b301da721c34ca1aca29ce2e4c7d71ae580b519a3332a4ba71870b6a58e |
| f67c6341bfe37f5b05c00a0dda738f472fdabd6ea94ca8dc761f57f11ce12036 |
| aed291c023c3514fb97b4e08e291e03f52de91a2a8d311491b4ab8299db0aa0f |
| faed55ed0102b1b2e3d853e8633abecbb9cec6a5f41c630097d8eaeefafba060 |
| C2: interestedthingsforkissinggirlwithloves[.]duckdns[.]org |
| C2: freebirdkissingonmylipswithnicefeelings[.]duckdns[.]org |
| AsyncRAT |
| b8fc29c02005c84131f34de083c2e81cdf615ff405877f9e73400bf35513c053 |
| 2d4ab87f9ea104075d372f4c211b1fb89adec60208d370b8fb2d748e1a73186c |
| b2e8f720740bbd46f6ae3f450f265ace1044fe232141fbd84f269eafeb290812 |
| a582e7e5b3ac37895e7cf484aaa8ea477deb90d99b47b2d9bfc018c604573889 |
| C2: 148[.]113[.]214[.]176 |
Detections:
Backdoor.Remcos
Backdoor.MsilFC.S13564499
Trojan.loaderCiR
MITRE ATTACK TTPs:
| Tactic | Technique ID | Name |
| Initial Access (TA0001) | T1566 | Phishing |
| Execution (TA0002) |
T1204 |
User Execution |
| Persistence (TA0003) | T1547.001 | Registry Run Keys/ Startup Folder |
| Defense Evasion (TA0005) | T1055 | Process Injection |
| T1027 | Obfuscated Files or Information | |
| T1036.004 | Masquerading Task or Service | |
| Discovery (TA0007) | T1614 | System Location Discovery |
| Exfiltration (TA0010) | T1041 | Exfiltration Over Command-and-Control Channel |
| Command and Control (TA0011) | T1001.0012 | Steganography |
Conclusion:
In this blog, we discussed the full attack-chain of the recent Steganographic campaign, where a harmless looking JPG file was revealed to be containing an injector DLL with malicious capabilities. We also explored how each malicious payload was carefully downloaded and executed in a highly methodical manner. The attack relied heavily on sophisticated masquerading techniques that can often deceive even experienced users. As is common, the chain of events began with a phishing email that contained an exploit which through multiple stages, ultimately deployed RemcosRAT/AsyncRAT (with the potential for other RATs or backdoors to be distributed in a similar manner). The command-and-control server, in this case, has the capability to deploy additional payloads, further compromising the victim’s system.
This campaign highlights the critical importance of remaining vigilant and adopting robust cybersecurity practices to safeguard both our safety and the integrity of our data.
Author:
Kirti Kshatriya
Co-Author:
Manoj Kumar Neelamegam
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