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Authored by By Yashvi Shah
McAfee Labs have recognized a rise in Wextract.exe samples, that drop a malware payload at a number of phases.
Wextract.exe is a Home windows executable file that’s used to extract recordsdata from a cupboard (.cab) file. Cupboard recordsdata are compressed archives which are used to bundle and distribute software program, drivers, and different recordsdata. It’s a official file that’s a part of the Home windows working system, and it’s positioned within the System32 folder of the Home windows listing. Nevertheless, like different executable recordsdata, it may be susceptible to exploitation by malicious actors who would possibly use it as a disguise for malware.
Some frequent ways in which malicious actors use a pretend or modified model of wextract.exe embrace:
Malware Distribution: Malicious actors can use a pretend model of the wextract.exe to ship malware onto a sufferer’s laptop. They’ll disguise the malware as a official file and use the pretend wextract.exe to extract and execute the malicious code.
Data stealing: A pretend or modified wextract.exe can be utilized to steal delicate info from a sufferer’s laptop. Malicious actors can modify the code to incorporate keyloggers or different data-stealing strategies.
Distant Entry: Malicious actors can use a pretend wextract.exe to achieve distant entry to a sufferer’s laptop. They’ll use the modified wextract.exe to create a backdoor or set up a distant connection to the sufferer’s laptop, permitting them to hold out varied malicious actions.
Ransomware Supply: Malicious actors can use a pretend or modified “wextract.exe” to put in ransomware on a sufferer’s system. For instance, they might create a pretend Home windows Installer bundle that seems to be a official software program replace or utility but in addition features a modified “wextract.exe” that encrypts the sufferer’s recordsdata and calls for a ransom cost for his or her decryption.
McAfee Labs collected malicious wextract.exe samples from the wild, and its habits was analyzed.
This weblog supplies an in depth technical evaluation of malicious “wextract.exe” that’s used as a supply mechanism for a number of sorts of malwares, together with Amadey and Redline Stealer. It additionally supplies detailed info on the strategies utilized by the malware to evade detection by safety software program and execute its payload. As soon as the malware payloads are executed on the system, they set up communication with a Command and Management (C2) server managed by the attacker. This communication permits the attacker to exfiltrate information from the sufferer’s system, together with delicate info resembling login credentials, monetary information, and different private info.
Determine 1: Attribute of the file
The file is a 32-bit Transportable Executable file, which is 631.50 Kb in measurement. The unique title of the file is WEXTRACT.EXE.MUI. The file description is “Самоизвлечение CAB-файлов Win32”, written in Russian, and means “Self-Extracting Win32 CAB Information”. The authorized copyright mentions Microsoft Company. Lots of static strings of this file had been discovered to be written in Russian.
Usually, the useful resource part (.rsrc) comprises assets utilized by this system, resembling icons, bitmaps, strings, and dialog bins. Attackers leverage the useful resource part of a PE file to enhance the success of their assaults by evading detection, enhancing persistence, and including performance.
The useful resource part of this pattern has multiples recordsdata, out of which CABINET useful resource holds 75.75% of the entire file, which makes the mentioned useful resource suspicious.
Determine 2: Sources within the file
A CAB (Cupboard) file is a compressed archive file format that’s usually used to compress and bundle a number of recordsdata right into a single file for distribution or set up. A CAB file within the useful resource part of a PE file can be utilized for varied functions resembling storing further program recordsdata or information, together with language-specific assets, or compressing and storing generally used assets to scale back the dimensions of the executable.
The CABINET holds two executables, cydn.exe and vona.exe.
Determine 3: CABINET in useful resource part
Likewise, below RCDATA, there may be one other attribute referred to as “RUNPROGRAM”, which begins cydn.exe. RUNPROGRAM within the useful resource part of a malware file sometimes refers to a useful resource that comprises directions for the malware to execute a particular program or command. When the malware is executed, it’s going to load the useful resource containing the “RUNPROGRAM” command and try to execute the desired program or command. This system is usually utilized by malware authors to execute further malicious packages or instructions on the contaminated system. For instance, the “RUNPROGRAM” useful resource might comprises directions to obtain and execute further malware, or to launch a malicious script or command that may carry out varied malicious actions resembling stealing delicate information, creating backdoors, or disabling safety software program.
Determine 4: RUNPROGRAM attribute stating “cydn.exe”
Like RUNPROGRAM, POSTRUNPROGRAM additionally holds the instruction to run the executable after RUNPROGRAM is executed. Therefore, as soon as cydn.exe is executed, vona.exe will likely be executed.
Determine 5: POSTRUNPROGRAM stating “vona.exe”
As soon as WEXTRACT.exe is executed, each cydn.exe and vona.exe is dropped within the TEMP folder. The TEMP folder is a generally used location for malware to retailer short-term recordsdata and different information, as it’s sometimes writable by any person account and isn’t often topic to strict safety restrictions. This will make it simpler for the malware to function with out elevating suspicion or triggering safety alerts.
Determine 6: Information dropped in TEMP folder
Stage 2: Evaluation of cydn.exe
The file confirmed excessive file ratio of the useful resource part, with the entropy of seven.810. Entropy is a measure of the randomness or unpredictability of the info within the file. It’s usually used as an indicator of whether or not a file is more likely to be malicious or not.
Within the case of a PE file, excessive entropy can point out that the file comprises a big quantity of compressed or encrypted information, or that it has been obfuscated or packed in a approach that makes it tougher to investigate. This generally is a frequent method utilized by malware authors to evade detection by antivirus software program.
Determine 7: File ratio and entropy of the useful resource part
Just like the earlier file, cydn.exe additionally had two executables archived in its useful resource part, named aydx.exe and mika.exe. The “RUNPROGRAM” attribute instructions to run aydx.exe and the “POSTRUNPROGRAM” attribute instructions to execute mika.exe as soon as aydx.exe is executed. These recordsdata are additionally dropped in TEMP folder.
Determine 8: aydx.exe and mika.exe packed in useful resource part
Determine 9: Executables dropped in one other TEMP folder
The order of file execution is as follows: First, Wextract.exe and cydn.exe, which have already been mentioned, are adopted by aydx.exe, after which by mika.exe and vona.exe.
Determine 10: Execution stream
Stage 3: Evaluation of aydx.exe
Aydx.exe is a 32-bit Transportable Executable file, which is 405Kb and is compiled in C/C++. As soon as executed, it makes an attempt to make a request to IP handle: 193.233.20.7.
Determine 11: Malware making an attempt to hook up with IPv4
This IP handle is linked with Redline Stealer connecting on port quantity 4138.
Evaluation of mika.exe
Mika.exe is 32-bit Transportable Executable, complied in .NET and is simply 11 KB in measurement. The unique title of the file is “Healer.exe”. This exe file makes no web exercise however does one thing within the goal machine which assists malwares from additional phases to hold out their execution.
The intent of mika.exe is to show off Home windows Defender in all doable methods. As soon as mika.exe was executed, that is how the Defender settings of the system appeared like:
Determine 12: Actual-time safety turned off
This setting was irreversible and couldn’t be turned again to on through settings of Home windows. Following this, logs from Procmon had been analyzed and there have been entries relating to Home windows defender, resembling:
Determine 13: Procmon logs
To validate this, Registry was analysed and all of the adjustments had been discovered there. The adjustments in Registry had been discovered to be in precise order as of Procmon logs. In Home windows, the registry is a hierarchical database that shops configuration settings and choices for the working system, in addition to for purposes and units. It’s used to retailer details about the {hardware}, software program, person preferences, and system settings on a Home windows laptop. Following keys are added below Actual-Time Safety:
DisableBehaviourMonitoring
DisableIOAVProtection
DisableOnAccessProtection
DisableRealtimeMonitoring
DisableScanOnRealitimeEnable
Determine 14: Keys added in Registry
By doing so malware is limiting all the traditional customers from turning the Home windows Defender on. When attackers disable Home windows Defender by way of the registry, the change is more likely to persist even when the person or administrator tries to re-enable it by way of the Home windows Defender settings. This enables the attacker to keep up management over the system for an extended interval. This helps malwares of additional phases to simply execute themselves with none hinderances. This may be leveraged by all of the malwares, no matter their correspondence to this very marketing campaign.
Stage 4: Evaluation of vona.exe
Vona.exe, a variant of the Amadey malware household, is compiled in C/C++ and is 236 KB in measurement. That is the final file to be executed from the present cluster. When executed, a extremely in depth course of tree shortly appeared.
Determine 15: Course of tree of vona.exe
Stage 5: Evaluation of mnolyk.exe
A right away youngster strategy of vona.exe is mnolyk.exe, one other Amadey part, is dropped in a folder in TEMP folder.
Determine 16: mnolyk.exe dropped in TEMP folder
Mnolyk.exe makes lively connections to IP addresses 62.204.41.5 and 62.204.41.251
Malicious DLLs are downloaded from 62.204.41.5, that are executed later within the marketing campaign. The goal was made to seek for two completely different DLLs, particularly cred.dll and clip.dll.
Determine 17: Malicious dlls downloaded
From 62.204.41.251, varied exe recordsdata are downloaded to the TEMP folder, and later executed. Exes downloaded are:
fuka.exe
Determine 18: fuka.exe
nikas.exe
Determine 19: nikas.exe
igla.exe
Determine 20: igla.exe
nocr.exe
Determine 21: nocr.exe
lebro.exe
Determine 22: lebro.exe
Following the execution of mnolyk.exe, a collection of schtasks.exe and cacls.exe had been executed.
The command line for schtasks.exe is “C:WindowsSystem32schtasks.exe” /Create /SC MINUTE /MO 1 /TN mnolyk.exe /TR “C:UserstestAppDataLocalTemp5eb6b96734mnolyk.exe” /F
“/Create” – That is the command to create a brand new scheduled job.
“/SC MINUTE” – This parameter units the scheduling interval for the duty to “MINUTE”. The duty will run each minute.
“/MO 1” – This parameter units the repeat rely to “1”. The duty will run solely as soon as.
“/TN” – This parameter specifies the title of the duty. The title ought to be specified after the “/TN” parameter.
So, the complete command line “schtasks.exe /Create /SC MINUTE /MO 1 /TN” would create a scheduled job that runs as soon as each minute. The title of the duty specified is the trail to mnolyk.exe.
There have been a number of situations of cacls.exe created. One in every of them is defined right here together with its parameter. The command line is “CACLS ”mnolyk.exe” /P “take a look at:R” /E”
“CACLS” – That is the command to alter the ACL of a file.
“mnolyk.exe” – That is the file for which the ACL will likely be modified.
“/P take a look at:R” – This parameter specifies the permission change for a person named “take a look at”. The “:R” on the finish signifies that the “take a look at” person will likely be granted “Learn” permission.
“/E” – This parameter specifies that the ACL change will likely be made to the file’s efficient ACL. The efficient ACL is the precise set of permissions which are utilized to the file.
So, the complete command line “CACLS mnolyk.exe /P take a look at:R /E” would grant the “take a look at” person or group “Learn” permission to the “mnolyk.exe” file. Therefore the person “take a look at” can neither write nor delete this file. If rather than “/P take a look at:R”, “/P take a look at:N” was talked about, which is talked about in one of many command line, it will give “None” permission to the person.
Stage 6: Analyzing fuka.exe, nikas.exe, igla.exe, nocr.exe and lebro.exe
Fuka.exe
Fukka.exe, a variant of the Redline Stealer malware household, is 175 KB and is compiled in .NET. The unique title of the file is Samarium.exe. It exhibits some community exercise with IP 193.233.20.11.
Determine 23: Community exercise of fuka.exe
Nikas.exe
Nikas.exe is 248 KB executable file compiled in C/C++. It disables automated updates for Home windows and checks the standing of all of the sub-fields of Actual-Time Safety that had been beforehand modified by mika.exe. No community exercise was discovered throughout replication.
Igla.exe
Igla.exe is 520 KB file, compiled in C/C++. The unique title of the file is WEXTRACT.EXE.MUI. Like we noticed in cydn.exe, this PE has additionally two extra exes packed in its useful resource part, bvPf.exe and cmkmka.exe. As soon as igla.exe is executed, bvPf.exe is executed, adopted by cmkmka.exe.
Determine 24: RUNPROGRAM attribute in igla.exe
Determine 25: POSTRUNPROGRAM attribute in igla.exe
bvPf.exe
bvPf.exe is 306 KB in measurement and is compiled in C/C++. The unique filename is nightskywalker.exe. The file is dropped in a folder in TEMP folder of the system.
The exe has tried connecting to 193.233.20.11, however server didn’t reply, and no communication befell.
cmkmka.exe
cmkmka.exe is 32-bit PE file, 283.5 KB in measurement. It additional launches AppLaunch.exe which communicates to C2.
It communicates to the IP handle: 176.113.115.17 which is an lively C2 for Redline Stealer and connects to the port 4132.
Determine 26: Information exfiltration
The blue-colored content material within the information signifies the knowledge being transmitted from the Command and Management (C2) server, which is offering directions to the malware relating to the precise information that must be retrieved together with their corresponding paths. These paths embrace person profiles of various internet browsers, varied crypto pockets paths, and different associated information.
As a response, all the info residing on the specified paths is shipped again to the C2 server of the malware. This contains all of the profiles of various internet browsers, info associated to crypto wallets, and even user-related information from the Home windows working system. This course of permits the C2 server to gather an enormous quantity of delicate info from the contaminated system, which might be exploited by the attackers for malicious functions.
Nocr.exe
Nocr.exe, a part of Redline Stealer, is a 175 KB .NET binary. The unique title of the file is Alary.exe. It communicates to the IP handle 176.113.115.17.
Lebro.exe
Lebro.exe, a part of Amadey, is a 235 KB file, compiled in C/C++. Lebro.exe is accountable for executing nbveek.exe, which is a subsequent stage of the malware. The file is once more dropped in TEMP folder.
Determine 27: Dropping one other executable in TEMP folder
Stage 7: Analyzing nbveek.exe
The hashes of lebro.exe and nbveek.exe are similar, they’re the identical binaries, therefore it’s Amadey. It’s connecting to IP 62.204.41.88.
Determine 28: Community exercise of nbveek.exe
The goal system executes a php file, and the content material of file contains the command to obtain one other exe referred to as setupff.exe. This exe is downloaded to the TEMP folder.
Earlier than setupff.exe is executed, once more the collection of schtasks.exe and cacls.exe are executed which had been seen beforehand additionally. The identical parameters had been handed for nbveek.exe as they had been for mnolyk.exe.
Setupff.exe
Setupff.exe is compiled in C/C++ and is 795 KB. The file couldn’t execute and threw Home windows error.
Stage 8: Remaining stage
Later, one other occasion of setupff.exe was created which additional invokes a number of situations of rundll32.exe. Right here, the 2 dlls downloaded by mnolyk.exe, clip64.dll and cred64.dll, are executed by way of rundll32.exe. McAfee Labs detects these dlls to be Amadey maware.
The community exercise exhibits the dll to be connecting to 62.204.41.88. This dll once more begins exfiltrating information to C2:
Determine 29:Information exfiltration
To conclude, the risk posed by the multi-stage assault that drops the Amadey botnet, and subsequently Redline Stealer, is critical and requires fixed vigilance from each shoppers and safety professionals. Through the use of the Amadey botnet as a supply mechanism for different malware, attackers can leverage these similar capabilities to evade detection and keep persistence on contaminated computer systems. They’ll use Amadey to drop a variety of malware, resembling adware, ransomware, and trojans, which can be utilized for quite a lot of malicious functions, resembling stealing delicate info, encrypting recordsdata for ransom, or taking management of a pc to be used in a bigger botnet. Our evaluation of assorted samples of this assault has revealed that the Amadey botnet distributes malware from a number of households and isn’t restricted to Redline Stealer alone.
At McAfee, we’re dedicated to offering our prospects with sturdy and efficient antivirus and anti-malware options that may detect and defend in opposition to threats just like the Amadey botnet and different malware households. Our safety software program makes use of a mix of signature, machine studying, risk intelligence and behavioral-based detection strategies to determine and cease threats earlier than they will trigger harm.
Indicators of Compromise (IOCs):
File Sort
SHA-256
Product
Detection
.exe
80fed7cd4c7d7cb0c05fe128ced6ab2b9b3d7f03edcf5ef532c8236f00ee7376
Complete Safety and LiveSafe
Downloader-FCNDLockbit-FSWWPWS-FDON
.exe
d8e9b2d3afd0eab91f94e1a1a1a0a97aa2974225f4f086a66e76dbf4b705a800
Complete Safety and LiveSafe
PWS-FDONLockbit-FSWW
.exe
1d51e0964268b35afb43320513ad9837ec6b1c0bd0e56065ead5d99b385967b5
Complete Safety and LiveSafe
Lockbit-FSWW
.exe
850cd190aaeebcf1505674d97f51756f325e650320eaf76785d954223a9bee38
Complete Safety and LiveSafe
PWS-FDON
.exe
6cbcf0bb90ae767a8c554cdfa90723e6b1127e98cfa19a2259dd57813d27e116
Complete Safety and LiveSafe
Downloader-FCND
.exe
6cbcf0bb90ae767a8c554cdfa90723e6b1127e98cfa19a2259dd57813d27e116
Complete Safety and LiveSafe
Downloader-FCND
.exe
8020580744f6861a611e99ba17e92751499e4b0f013d66a103fb38c5f256bbb2
Complete Safety and LiveSafe
AgentTesla-FCYU
.exe
021ae2fadbc8bc4e83013de03902e6e97c2815ab821adaa58037e562a6b2357b
Complete Safety and LiveSafe
Lockbit-FSWW
.exe
aab1460440bee10e2efec9b5c83ea20ed85e7a17d4ed3b4a19341148255d54b1
Complete Safety and LiveSafe
Lockbit-FSWW
.exe
54ce28a037eea87448e65bc25f8d3a38ddd4b4679516cc59899b77150aa46fcc
Complete Safety and LiveSafe
GenericRXVK-HF
.exe
0cca99711baf600eb030bbfcf279faf74c564084e733df3d9e98bea3e4e2f45f
Complete Safety and LiveSafe
AgentTesla-FCYU
.exe
ad1d5475d737c09e3c48f7996cd407c992c1bb5601bcc6c6287eb80cde3d852b
Complete Safety and LiveSafe
Downloader-FCND
.exe
ad1d5475d737c09e3c48f7996cd407c992c1bb5601bcc6c6287eb80cde3d852b
Complete Safety and LiveSafe
Downloader-FCND
.exe
d40d2bfa9fcbf980f76ce224ab6037ebd2b081cb518fa65b8e208f84bc155e41
Complete Safety and LiveSafe
GenericRXVJ-QP
.dll
cdd4072239d8a62bf134e9884ef2829d831efaf3f6f7f71b7266af29df145dd0
Complete Safety and LiveSafe
PWS-FDOE
.dll
10ee53988bcfbb4bb9c8928ea96c4268bd64b9dfd1f28c6233185e695434d2f8
Complete Safety and LiveSafe
Trojan-FUUW
.dll
3492ed949b0d1cbd720eae940d122d6a791df098506c24517da0cc149089f405
Complete Safety and LiveSafe
Trojan-FUUW
IPv4
193.233.20.7
IPv4
62.204.41.5
IPv4
62.204.41.251
IPv4
193.233.20.11
IPv4
176.113.115.17
IPv4
62.204.41.88
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