New SysJoker Backdoor Targets Windows, Linux, and macOS

The malware is written in C++ and each sample is tailored for the specific operating system it targets.
Both the macOS and Linux samples are fully undetected in VirusTotal.
ysJoker’s behavior is similar for all three operating systems. analysts will analyze SysJoker’s behavior on Windows.

Unlike Mac and Linux samples, the Windows version contains a first-stage dropper. The dropper (d71e1a6ee83221f1ac7ed870bc272f01) is a DLL that was uploaded to VirusTotal as style-loader.ts and has only 6 detections at the time of this writing.

The Dropper drops a zipped SysJoker (53f1bb23f670d331c9041748e7e8e396) from C2 https[://]github[.]url-mini[.]com/msg.zip, copies it to C:ProgramDataRecoverySystemrecoveryWindows.zip, unzips it and executes it. All of these actions are executed via PowerShell commands.

Once SysJoker (d90d0f4d6dad402b5d025987030cc87c) is executed it sleeps for a random duration between 90 to 120 seconds. Then, it will create the C:ProgramDataSystemData directory and copy itself under this directory, masquerading as igfxCUIService.exe (igfxCUIService stands for Intel Graphics Common User Interface Service). Next, it will gather information about the machine using Living off the Land (LOtL) commands.
SysJoker uses different temporary text files to log the results of the commands. These text files are deleted immediately, stored in a JSON object, and then encoded and written to a file named microsoft_windows.dll.

It will gather the MAC address, user name, physical media serial number, and IP address (see IoCs section for the full commands list). SysJoker will create persistence by adding an entry to the registry run key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun. Between each of the steps above, the malware sleeps for a random duration.

Next, SysJoker will begin its C2 communication.
SysJoker holds within the binary a hardcoded XOR key which is used for decoding and encoding strings from within the binary and data sent and received from the C2. The XOR key is an RSA public key that is not used in the decoding scheme.
The same XOR key exists in all versions of SysJoker:

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDkfNl+Se7jm7sGSrSSUpV3HUl3vEwuh+xn4q

BY6aRFL91x0HIgcH2AM2rOlLdoV8v1vtG1oPt9QpC1jSxShnFw8evGrYnqaou7gLsY5J2B06eq5UW7

+OXgb77WNbU90vyUbZAucfzy0eF1HqtBNbkXiQ6SSbquuvFPUepqUEjUSQIDAQAB

The Google Drive link hosts a text file named domain.txt that holds an encoded C2. The text file’s content changes over time, depending on the current available C2. SysJoker will decode the C2 and send the collected user’s information to the C2’s /api/attach directory as an initial handshake.
The C2 replies with a unique token which will be used as an identifier from now on when the malware communicates with the C2.

SysJoker runs a while(1) loop that sends a request to the C2’s /api/req directory with the unique token and will process the C2’s response which is built as JSON using functions from this library.
If the server responds with data, SysJoker will parse the received payload (see step 3 in the image below). SysJoker can receive the following instruction from the C2: exe, cmd, remove_reg, and exit.
remove_reg and exit are not implemented in this current version. Based on the instruction names, analysts can assume that they are in charge of self-deletion of the malware. Let’s look into exe and cmd instructions:
exe – This command is in charge of dropping and running an executable.
SysJoker will receive a URL to a zip file, a directory for the path the file should be dropped to, and a filename that the malware should use on the extracted executable.
It will download this file, unzip it and execute it.
After execution, the malware will reply to the C2’s /api/req/res API with either “success” if the process went successful or “exception” if not.

Sign Up For Threat Alerts

Loading...
Threats Icon

May 25, 2022

Twisted Panda: Chinese APT espionage operation against...

Check Point Research (CPR) details a targeted campaign that has been using sanctions-related baits to...

Threats Icon

May 23, 2022

A deeper look at XorDdos malware targeting...

In the last six months, we observed a 254% increase in activity from a Linux...

Threats Icon

May 22, 2022

Ransomware Spotlight RansomEXX

RansomEXX is another ransomware variant that runs on a ransomware-as-a-service (RaaS) model and has been...

Threats Icon

May 19, 2022

Malicious Compiled HTML Help File Delivering Agent...

PaloAlto Unit42 discovered a malicious HTML help file delivering Agent Tesla. The attack is interesting...

Threats Icon

May 16, 2022

BPFdoor: Stealthy Linux malware bypasses firewalls for...

A recently discovered backdoor malware called BPFdoor has been stealthily targeting Linux and Solaris systems...

Threats Icon

May 16, 2022

Onyx ransomware destroys files instead of encrypting...

A new Onyx ransomware operation is destroying files larger than 2MB instead of encrypting them,...

Threats Icon

May 15, 2022

Researchers Warn of Nerbian RAT Targeting Entities...

A previously undocumented remote access trojan (RAT) written in the Go programming language has been...

Threats Icon

May 12, 2022

Bitter APT targets Bangladesh

Cisco Talos has observed an ongoing malicious campaign from the Bitter APT group that appears...

Threats Icon

May 11, 2022

Experts Sound Alarm on DCRat Backdoor Being...

Cybersecurity researchers have shed light on an actively maintained remote access trojan called DCRat (aka...

Threats Icon

May 11, 2022

The Lotus Panda is awake, again

In this attack analyzed by C25, the Chinese APT used a spear phishing email to...

Threats Icon

May 09, 2022

Moshen Dragon – Abusing Security Software to...

SentinelLabs recently uncovered a cluster of activity targeting the telecommunication sector in Central Asia, utilizing...

Threats Icon

May 09, 2022

AvosLocker Ransomware Abuses Driver File to Disable...

TrendMicro found samples of AvosLocker ransomware that makes use of a legitimate driver file to...

Threats Icon

May 02, 2022

LockBit Ransomware Side-loads Cobalt Strike Beacon

The VMware command line utility VMwareXferlogs.exe used for data transfer to and from VMX logs...

Threats Icon

May 02, 2022

Emotet Returns With New TTPs And Delivers...

The epoch4 Emotet server started spamming and delivering zipped .lnk files to its victims through...

Threats Icon

Apr 28, 2022

BRONZE PRESIDENT

Government-sponsored threat actors collect intelligence to benefit their country, and changes to the political landscape...