Uncovering the “Serpent”

Malware Analysis
1

Information Stealers are a pervasive threat and are capable of providing threat actors with a rich source of sensitive data. 

Recently, we came across this tweet that the Serpent Stealer is on sale on the dark web. A .NET based malware, this has the ability to not only acquire sensitive information from the most popular online browsers and applications but also has the capability to exfiltrate  passwords.  

Figure 1: Tweet about Serpent Stealer

To stay stealth, the stealer bypasses Windows User Access Control (UAC), debuggers, and virtual machines. It exfiltrates the browser data and passwords via Web hooks and Discord abuse. 

Binary Analysis

Serpent is a .Net based stealer that utilises the .NET runtime. It is a 64-bit portable executable binary.

Figure 2: File info (Serpent_Stealer)

The procedures within the Main() function of the malware binary, employed for data theft, has been systematically presented below based on their execution sequence.

Figure 3: Main Function

Environment checks

The stealer determines whether it is being run in a controlled environment on its first execution. It does that by checking whether the victim’s username-obtained exists in its “Black List Users” file.

The usernames that are blocked are shown in the table below. The stealer will instantly utilise the Sleep and Exit function to end its execution if any of the below usernames are obtained.

Figure 4: Iterating with blacklist username

05h00Gi0 3u2v9m8 43By4 4tgiizsLimS 6O4KyHhJXBiR
7wjlGX7PjlW4 8Nl0ColNQ5bq 8VizSM Abby Amy
AppOnFlySupport ASPNET azure BUiA1hkm BvJChRPnsxn
cM0uEGN4do cMkNdS6 DefaultAccount dOuyo8RV71 DVrzi
e60UW ecVtZ5wE EGG0p Frank fred
G2DbYLDgzz8Y george GjBsjb Guest h7dk1xPr
h86LHD Harry Johnson HEUeRzl hmarc ICQja5iT
IVwoKUF j6SHA37KA j7pNjWM John jude
Julia kEecfMwgj kFu0lQwgX5P KUv3bT4 Lisa
lK3zMR lmVwjj9b Louise Lucas mike
Mr.None noK4zG7ZhOf o6jdigq o8yTi52T OgJb6GqgK0O
patex Paul Jones pf5vj PgfV1X PqONjHVwexsS
pWOuqdTDQ PxmdUOpVyx QfofoG QmIS5df7u QORxJKNk
qZo9A RDhJ0CNFevzX RGzcBUyrznReg S7Wjuf server
SqgFOf3G Steve test TVM txWas1m2t
umyUJ Uox1tzaMO User01 w0fjuOVmCcP5A WDAGUtilityAccount
XMiMmcKziitD xPLyvzr8sgC ykj0egq7fze DdQrgc ryjIJKIrOMs
nZAp7UBVaS1 zOEsT l3cnbB8Ar5b8 xUnUy fNBDSlDTXY
vzY4jmH0Jw02 gu17B UiQcX 21zLucUnfI85 OZFUCOD6
8LnfAai9QdJR 5sIBK rB5BnfuR2 GexwjQdjXG IZZuXj
ymONofg dxd8DJ7c JAW4Dz0 GJAm1NxXVm UspG1y1C
equZE3J BXw7q lubi53aN14cU 5Y3y73 9yjCPsEYIMH
GGw8NR JcOtj17dZx 05KvAUQKPQ 64F2tKIqO5 7DBgdxu
uHUQIuwoEFU gL50ksOp Of20XqH4VL tHiF2T hbyLdJtcKyN1
katorres doroth umehunt sal.rosenburg PateX
Figure 5: Evasion Technique

Data collection

Once the malware verifies that it is not running under a controlled environment, it starts collecting data for exfiltration.

It begins with obtaining autofill information. The directory “%Localappdata%\\Google\\Chrome\\User Data ” is first obtained. After that it establishes connection with the SQLite database and collects data using the “SELECT * FROM autofill” query.

Figure 6: Autofill stealer

Next it collects history data from “%Localappdata%\\Google\\Chrome\\User data” path. After that it establishes connection with the SQLite database and collects data using the “SELECT url FROM urls” query.

Figure 7: History stealer

After this, it verifies the machine’s remote IP address. Then, it uses a webhook to exfiltrate the data it has collected to the C2 server.

Figure 8: Checks the Remote IP

Figure 9: Webhook – exfiltration technique

After communicating with C2 it tries to collect password data from any existing browser like Chrome, Brave or Edge browsers.

Figure 10: Password stealer

Next it targets crypto wallets by collecting some well-known crypto wallet software data.

Figure 11: Crypto wallet names

Figure 12: Collects wallet data

After collecting wallet data, it tries to collect bookmark data from Chrome browser,

Figure 13: Bookmark stealer

Afterward, the malware extracts login credentials from the installation path by identifying the registry path associated with Steam, a video game digital distribution service.

It also tries to steal SSH credentials from ‘.ssh’ directory and FTP credentials from the windows registry.

Figure 14: SSH stealer

Figure 15: FTP stealer

At last it runs a file stealer, which targets some specific extensions from some specific folders in the file system.

Figure 16: File stealer and the extensions targeted

The file stealer program target following directories,

  • Desktop
  • Documents
  •  Pictures
  • Videos
  • Downloads

UAC Bypass

Before exiting, stealer calls one of the UAC bypass methods listed below

  • GUI based Bypass
  • Bypass using Fodhelper
  •  Bypass using windows defender

Here, in the sample analysed,  they are using Fodhelper method,

Figure 17: UAC bypass

Fodhelper.exe is a known UAC bypass method, and when it runs, it looks for certain registry keys that do not exist. As a result, a hacker can insert malicious commands into these registry keys to be executed by the fodhelper.exe with the highest privilege(Admin privilege). 

  1. “New-Item “HKCU:\Software\Classes\ms-settings\Shell\Open\command” -Force” – This command creates a new registry key at the mentioned path in the registry.
  2. “New-ItemProperty -Path “HKCU:\Software\Classes\ms-settings\Shell\Open\command” -Name “Delegate Execute” -Value “” -Force” – This command adds a new registry entry named Delegate Execute with an empty string value to the key.
  3. “New-ItemProperty -Path “HKCU:\Software\Classes\ms-settings\Shell\Open\command” -Name “(default)” -Value \”{0}\” -Force” – This command sets the default value of the registry key in the mentioned path to the value specified in the {0} placeholder.
Figure 18: Program ending

As we can see, threat actors use advanced stealth techniques in info stealers to become more evasive. As the information stolen by the malware is sensitive, protecting yourself by investing in a reputable security product is therefore necessary in today’s world. We at K7 Labs provide detection for such kinds of stealers and all the latest threats. Users are advised to use a reliable security product such as “K7 Total Security” and keep it up-to-date to safeguard their devices.

IOCs

Hash Detection name
e97868c8431ccd922dea3dfb50f7e0b5 Password-Stealer  (005ac0721 )
a3c4785a011c350839669b8e73c823f5 Password-Stealer (005ac0721 )
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