What Is Initial Access?
Initial Access refers to the techniques adversaries use to gain a foothold inside a target environment. This foothold is the very first step of the attack chain, before persistence, lateral movement, privilege escalation, data theft, or disruption. In most real-world intrusions, if you understand how attackers got in, you understand how to prevent everything that comes next.
MITRE ATT&CK® defines Initial Access as a collection of methods adversaries use to penetrate a system or network for the first time. These attacks vary in sophistication, from simple phishing emails to exploiting unpatched public-facing systems, but they all share one goal: open the door.
How Initial Access Connects to Supply Chain (Third-Party) Risks
One of the fastest-growing vectors for Initial Access is the supply chain.
Attackers increasingly target vendors, service providers, software suppliers, or externally exposed assets associated with third parties. A weak vendor can become the path into a stronger, well-protected organization. This is because:
- Vendors often have remote access, shared credentials, or API integrations.
- Companies frequently rely on external services exposed on the open internet.
- A compromise of one supplier can cascade across all its customers.
- Third-party environments may have different patching cadences or security maturity.
A supply chain breach is itself an initial access technique, one that leverages trust relationships to bypass direct defenses. That’s why modern TPRM, ASM, and CTEM programs focus heavily on identifying externally exposed assets, vulnerabilities, and misconfigurations, not only for your organization, but for your vendors.
Initial Access Techniques (as defined and commonly referenced in MITRE ATT&CK®)
Initial access can occur through many different paths, and attackers choose their method based on opportunity, exposure, and the weakest point in the digital ecosystem, whether inside your environment or within your supply chain. The following techniques represent some of the most common and effective entry points adversaries exploit across IT, OT, cloud, and third-party environments:
- Drive-By Compromise
- Exploit Public-Facing Application
- Exploitation of Remote Services
- External Remote Services
- Internet-Accessible Device
- Remote Services
- Replication Through Removable Media
- Rogue Master
- Spearphishing
- Transient Cyber Asset
- Wireless Compromise
Each of these techniques reflects a different path attackers can take to gain their first foothold, some rely on human error, others target exposed infrastructure, while some exploit trusted relationships with vendors or contractors. To understand how adversaries operate and how organizations can defend against them, let’s break down each technique, what makes it effective, and where it fits within modern supply chain and third-party attack scenarios.
1. Drive-By Compromise
A drive-by compromise occurs when an attacker infects a website, often one that users trust, and waits for visitors to load it. When the victim accesses the site, malicious code automatically executes through browser vulnerabilities or hidden scripts.
Why it matters:
- Requires no user interaction beyond visiting a web page
- Effective for mass infections
- Hard to detect if the compromised site is legitimate
2. Exploit Public-Facing Application
This technique targets vulnerabilities in applications that are exposed to the internet, web servers, APIs, VPN portals, file-transfer solutions, and more.
Attackers probe these systems using automated scanners, exploit kits, or zero-days. If successful, they gain direct access to the server or the underlying OS.
Common weaknesses:
- Outdated frameworks
- Weak authentication
- Misconfigurations
- Vulnerable plugins
Supply chain link: Vendors hosting or maintaining these services may indirectly expose their customers.
3. Exploitation of Remote Services
Attackers exploit vulnerabilities or misconfigurations in remote execution services such as RDP, VNC, SSH, SMB, or custom remote management consoles.
This includes both:
- Exploiting a vulnerability (e.g., RDP exploit)
- Leveraging weak configurations (e.g., no MFA, outdated encryption, open ports)
Why it matters:
Remote services are a backbone of IT operations, making them a high-value target.
4. External Remote Services
This refers specifically to adversaries using legitimate remote access services (VPN, Citrix, cloud console, SaaS portals) to authenticate into the environment.
The access itself is valid, but obtained through:
- Password theft
- MFA fatigue attacks
- Credential stuffing
- Darknet data leaks
- Phishing
Supply chain angle: If a vendor’s credentials are stolen, the attacker now enters your network “as the vendor.”
5. Internet-Accessible Device
Attackers scan the internet for exposed devices, IoT, OT equipment, cameras, routers, printers, industrial control systems, and directly access them if they are misconfigured or vulnerable.
These devices often lack:
- Proper authentication
- Patching schedules
- Monitoring
Risk: Once inside, attackers pivot deeper into the network.
6. Remote Services
This is a broader category for any remote management or interactive service that provides access to internal systems.
While similar to External Remote Services, this focuses more on internal remote administration protocols rather than user-facing interfaces.
Examples:
- Remote PowerShell
- Management ports
- Hypervisor consoles
- Remote backup interfaces
Attackers who gain these accesses often jump directly into high-privilege environments.
7. Replication Through Removable Media
Think of this as modern malware that spreads via USB drives or portable media, similar to Stuxnet’s early propagation techniques.
Risk factors:
- Contractors plugging devices into secure networks
- Offline industrial systems relying on USB updates
- Air-gapped environments
This is still relevant in OT, defense, and isolated networks.
8. Rogue Master
In industrial or OT environments, a “rogue master” is a malicious system impersonating a legitimate controller. Attackers insert themselves into the control network to issue unauthorized commands.
Use cases:
- SCADA environments
- ICS protocols (e.g., Modbus)
- Manufacturing plants
- Critical infrastructure
This is one of the most dangerous forms of OT initial access.
9. Spearphishing
The classic, and still most successful, initial access vector.
Spearphishing involves sending targeted emails or messages containing:
- Malicious attachments
- Links to payloads
- Credential-harvesting sites
- Social engineering traps
Attackers often rely on intelligence collected from social media, job postings, or leaked vendor data to tailor the message.
Supply chain tie:
Threat actors frequently impersonate service providers or vendors to increase credibility.
10. Transient Cyber Asset
A transient cyber asset is a temporary device (like a contractor’s laptop, a vendor technician’s machine, or diagnostic equipment) connected only briefly to an environment.
Attackers may compromise these external devices to inject malware into the target during the short connection window.
This is especially relevant in:
- Industrial environments
- Healthcare devices
- On-site vendor workstations
11. Wireless Compromise
Attackers gain initial access by exploiting wireless networks, such as:
- Wi-Fi
- Bluetooth
- NFC
- Proprietary industrial wireless protocols
Tactics include:
- Cracking weak Wi-Fi passwords
- Setting up rogue access points
- Intercepting traffic
- Attacking misconfigured IoT wireless modules
Wireless compromises bypass physical perimeter defenses entirely.
Why Preventing Initial Access Delivers the Highest Security ROI
Most organizations spend enormous effort on detection and response once an attacker is already inside the network. But in reality, the most impactful place to stop a breach is before it begins, at the very first point of entry. That’s why strengthening defenses around Initial Access delivers some of the highest returns in cybersecurity: preventing the foothold prevents the entire attack chain.
Today, this challenge is even more complex because adversaries increasingly look beyond your own perimeter. They search for weaknesses in vendors, partners, hosted services, and any third-party system connected to your environment. In a world where every company relies on a network of suppliers and digital services, your exposure is directly shaped by the security of everyone you work with. Gaining clear visibility into your external attack surface and into the posture of your supply chain is essential to reducing real-world risk.