A close look at the advanced techniques used in a Malaysian-focused APT campaign

The Elastic Security Intelligence & Analytics Team researches adversary innovations of many kinds, and has recently focused on an activity group that leveraged remote templates, VBA code evasion, and DLL side-loading techniques. Based on code similarity and shared tactics, techniques, and procedures (TTPs), the team assessed this activity to be possibly linked to a Chinese-based group known as APT40, or Leviathan. The group’s campaign appears to target Malaysian government officials with a lure regarding the 2020 Malaysian political crisis.

Anatomy of the attack

To initiate their advanced persistent threat (APT) campaign, the group likely delivered a Microsoft Word document as a phishing lure attachment. The image used in the lure (Figure 2) appears to be crafted from a broadcast announcement shared by a Malaysian blogger (Figure 1). The lure image includes the same broadcast time, but the date and speech topic are removed. Once this attachment is opened, a decoy document is presented while behind the scenes, taking the following actions:

The lure document downloads the remote template RemoteLoad.dotm
The remote template executes VBA macro code
The VBA macro code unpacks and executes two embedded base64-encoded DLLs (sl1.tmp and sl2.tmp) to c:\users\public\

This technique is known as template injection, which you may recall from our Playing defense against Gamaredon Group blog post. This an effective approach used by adversaries to bypass perimeter controls such as email gateways.

Both embedded DLLs (sl1.tmp and sl2.tmp) are similar and export the same function names: RCT and RCP. The first DLL (sl1.tmp) is used to download a benign executable called LogiMailApp.exe and an associated library LogiMail.dll, and the second DLL (sl2.tmp) is used to execute LogiMailApp.exe, which automatically attempts to execute LogiMail.dll due to an inherent DLL search order vulnerability we’ll cover shortly.


File name	File type	Size (bytes)	MD5	Compile time
LogiMailApp.exe	Win32 EXE	311656	850a163ce1f9cff0367854038d8cfa7e	2012-09-26 22:13:13+00:00
LogiMail.dll	Win32 DLL	105984	b5a5dc78fb392fae927e9461888f354d	2020-06-03 04:08:29+00:00
sl1.tmp	Win32 DLL	3072	ccbdda7217ba439dfb6bbc6c3bd594f8	2019-11-29 17:15:29+00:00
sl2.tmp	Win32 DLL	3072	dbfa006d64f39cde78b0efda1373309c	2019-11-29 21:23:44+00:00

Table 1: Dropped files metadata

This implementation stood out to our researchers due to a behavioral idiosyncrasy:

The Microsoft Office application winword.exe loads sl1.tmp and sl2.tmp DLLs uses the LoadLibraryA method, which is moderately rare
These DLLs run explicit commands or install a payload from a URL using the CallWindowProcA method, which appears to be exceptionally rare
Both DLLs are deleted after execution

Embedded DLLs

The embedded DLLs, sl1.tmp and sl2.tmp, have very limited functionality — exporting the RCP and RCT functions. The RCP function implements the WinExec method to execute commands where the RCT function uses the URLDownloadToFileA method to download a file from a specified URL.

DLL side-loading a backdoor

LogiMailApp.exe, which is downloaded by sl1.tmp and executed by sl2.tmp, is vulnerable to a form of DLL search-order hijacking called side-loading, which automatically searches for and executes LogiMail.dll if found in the same directory. Forms of DLL search-order hijacking can be used with many third-party software applications. In this case, search-order hijacking was used to load a backdoor that exports the following notable functions:

The adversary-created binary LogiMail.dll exports the function DllGetClassObject that contains critical logic for the execution flow of this sample:

Download an AES-encrypted second stage object to %TEMP%~liseces1.pcs
Derive a 128-bit AES key and initialization vector from SHA256 of a hardcoded string
Read and decrypt %TEMP%~liseces1.pcs in memory using the ReadFile and CryptDecrypt functions
Delete %TEMP%~liseces1.pcs from disk

Second stage backdoor

The decrypted second stage backdoor is mapped into memory and then its original entry point (OEP) is called, thus bypassing successful detections based on file system scanning.

Both the payload staging server and the second stage infrastructure use dynamic DNS:

This payload supports the following capabilities:

Basic anti-debug checks
System and user discovery
Execution via command line
File discovery, upload, and download
Persistence via run registry
Encrypt C2 traffic using same AES key

Possible APT40/Leviathan connection

Earlier in the year, the Malaysian Computer Emergency Response Team (MyCERT) issued an advisory related to espionage activity targeting their country. The report listed different TTPs and included multiple samples and other technical indicators that align with a threat group known as APT40/Leviathan.

At a high level, this sample follows the continued trend of targeting Malaysian victims using specific TTPs such as remote templates, employing macros, using DLL side-loading techniques, and leveraging an in-memory implant with dynamic DNS for command and control. More specifically, the second stage implant from this lure shares unique strings and URL references and contains similar functionality that correlates with the previous reporting for APT40/Leviathan. With these similarities, our Intelligence & Analytics Team assesses with moderate confidence that this activity is linked to APT40/Leviathan.

Implant String Similarities with MyCERT Sample:

/list_direction
/post_document
/post_login
Open Remote File %s Failed For: %s
Open Pipe Failed %s
Download Read Path Failed %s
%02X-%02X-%02X-%02X-%02X-%02X
Software\Microsoft\Windows\CurrentVersion\Run
ntkd

Conclusion

In this post, we highlighted a recent sample that most likely represents the work of a highly organized adversary. Activity groups like this are significant for everyone to take notice of, if only because they represent a higher maturity level of post-exploit innovation. Their cutting edge TTPs today end up being everyone’s run of the mill tomorrow; it’s important to learn from these events.

We hope that by sharing some of these insights, we can help raise awareness and continue to focus on protecting the world's data from attack. To enable organizations further, we’ve added all the observed MITRE ATT&CK® techniques and indicators of compromise (IoCs) below.

MITRE ATT&CK® techniques

Indicators of Compromise (IOCs)

File names and paths

Bubar Parlimen.zip
Bubar Parlimen.docx
RemoteLoad.dotm
C:\Users\Public\sl1.tmp
C:\Users\Public\sl2.tmp
C:\Users\*\AppData\Local\Temp\~liseces1.pcs
C:\Users\*\AppData\Local\Microsoft\Office\LogiMailApp.exe
C:\Users\*\AppData\Local\Microsoft\Office\LogiMail.dll

Registry keys

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\ntkd

URLs

hxxps[:]//armybar[.]hopto[.]org/LogiMail.dll
hxxps[:]//armybar[.]hopto[.]org/LogiMailApp[.]exe
hxxps[:]//armybar[.]hopto[.]org/Encrypted
hxxp[:]//tomema.myddns[.]me/postlogin
hxxp[:]//tomema[.]myddns[.]me/list_direction
hxxp[:]//tomema[.]myddns[.]me/post_document

IPs

104[.]248[.]148[.]156
139[.]59[.]31[.]188

HTTPS certificate

74b5e317527c93539dbaaf84d6a61da92a56012a

Hashes

523cbdaf31ddc920e5b6c873f3ab42fb791fb4c9d1f4d9e6a7f174105d4f72a1
ab541df861c6045a17006969dac074a7d300c0a8edd0a5815c8b871b62ecdda7
145daf50aefb7beec32556fd011e10c9eaa71e356649edfce4404409c1e8fa30
93810c5fd9a287d85c182d2ad13e7d30f99df76e55bb40e5bc7a486d259810c8
925f404b0207055f2a524d9825c48aa511199da95120ed7aafa52d3f7594b0c9
feca9ad5058bc8571d89c9d5a1eebce09e709cc82954f8dce1564e8cc6750a77
06a4246be400ad0347e71b3c4ecd607edda59fbf873791d3772ce001f580c1d3
77ef350639b767ce0a748f94f723a6a88609c67be485b9d8ff8401729b8003d2

YARA

rule APT_APT40_Implant_June2020 {
   meta:
       version = "1.0"
       author =  "Elastic Security"
       date_added = "2020-06-19"
       description = "APT40 second stage implant"
    strings:
        $a = "/list_direction" fullword wide
        $b = "/post_document" fullword wide
        $c = "/postlogin" fullword wide
        $d = "Download Read Path Failed %s" fullword ascii
        $e = "Open Pipe Failed %s" fullword ascii
        $f = "Open Remote File %s Failed For: %s" fullword ascii
        $g = "Download Read Path Failed %s" fullword ascii
        $h = "\\cmd.exe" fullword wide
    condition:
        all of them
}

A close look at the advanced techniques used in a Malaysian- focused APT campaign