🚪 MITRE ATT&CK: Tactic TA0001 — Initial Access: how attackers get in, the common ways, and what defenders should do

Initial Access (TA0001) is the very first step attackers take — gaining a foothold inside your environment so they can run the rest of their playbook. Below I list the common Initial Access techniques from the MITRE ATT&CK framework, explain each briefly, and give concrete prevention, detection, and response recommendations you can apply today.

What counts as “Initial Access”?

Initial Access = any technique an adversary uses to get into your network or systems in the first place. It’s usually the outcome of Reconnaissance and Resource Development (finding a target and preparing tooling), and it sets up everything that follows (persistence, lateral movement, exfiltration).

Common Initial Access techniques (what to watch for)

Below are the core techniques MITRE classifies under TA0001, with a short description of each.

• Exploit Public-Facing Application (T1190) — attackers exploit vulnerabilities in internet-exposed apps (CMS, VPNs, mail servers, etc.) to gain access. Patch and WAF gaps are often abused.

• Drive-by Compromise / Drive-by Download (T1189) — a user visits a malicious or compromised website and gets code executed (browser, plugin, or OS exploit).

• Phishing / Spearphishing (attachments, links, service, voice) — social engineering aimed at users to steal credentials, convince execution of malware, or get MFA bypassed. This includes spearphishing via service and voice phishes.

• External Remote Services / Remote Services (VPN, RDP, Citrix, etc.) — gaining access by abusing exposed remote access services or stolen/weak credentials for those services.

• Valid Accounts (T1078) — using compromised/legitimate credentials (service or user) to authenticate and enter the environment.

• Supply Chain Compromise (T1195) — tampering with software, hardware, vendor builds or delivery mechanisms so an adversary is introduced before the product reaches you.

• Replication Through Removable Media (T1091) — malware on USBs or other media that jumpstarts an infection (still a real risk for offline/air-gapped systems).

• Trusted Relationship / Hardware Additions / Other vector variants — attackers can leverage third-party vendor access, malicious hardware inserted into environments, or abuse of trusted integrations. (MITRE documents multiple related techniques and subtechniques).

(Note: MITRE periodically adds or refines techniques/sub-techniques — always check the live ATT&CK pages for the canonical list.) 

Recommendations — Prevent, Detect, Respond (practical, prioritized)

Prevent (stop the door from opening)

1. Patch & reduce attack surface

   • Prioritize patching internet-facing systems (web servers, CMS, Exchange, VPN appliances). Keep a prioritized CVE remediation process. Use virtual patching / WAF rules when immediate patching isn’t possible.

2. Harden remote access & require MFA

   • Enforce strong authentication (MFA) for VPN, cloud consoles, RDP/Citrix, and privileged accounts. Restrict administrative access to jump boxes and use just-in-time/zero-trust controls.

3. Email and web defenses

   • Deploy email filtering, attachment sandboxing, link rewriting, and anti-phishing training. Use secure browsing policies, block known malicious sites, and enforce least privilege for browser plugins.

4. Supply-chain controls

   • Vet and monitor third-party vendors, require SBOMs where available, validate software builds and vendor updates, and apply network segmentation to isolate vendor connections.

5. Disable unused services and autorun

   • Disable Autorun on removable media, close unused ports, and minimize exposed services. Inventory and remove legacy or forgotten internet-facing services.

6. Least privilege & account hygiene

   • Remove unnecessary accounts, enforce strong password policies, rotate service credentials, and disable default or unused accounts. Monitor for shared local admin accounts.
     

Detect (how to spot an initial access event early)

1. Log everything relevant and centralize

   • Collect logs from perimeter devices, VPNs, web servers, authentication systems, EDR telemetry, and cloud provider logs. Centralize in SIEM/analytics.

2. Hunt for early indicators

   • Examples of high-value detections / hunts:

     • Unexpected successful authentication from new locations to VPN/RDP.

     • Exploit-style indicators on web servers (sudden code drops, suspicious POSTs to upload endpoints).

     • New or uncommon processes spawned by web server user contexts.

     • Authentication with MFA bypass patterns or use of legacy protocols.

   • Threat hunting playbooks and queries help; MITRE/industry blogs publish recommended hunts.

3. EDR + network detection

   • Use EDR to detect process anomalies, persistence artifacts, suspicious child processes (e.g., web server spawning shell), and unusual use of administration tools. Network monitoring can spot beaconing or unusual external connections soon after initial access.

4. Email/link sandboxing telemetry

   • Monitor blocked/quarantined mails, unusual user clicks on rewritten links, and sandbox detonations. These often indicate targeted phishing attempts.

Respond (contain and remediate initial access)

1. Contain quickly and preserve evidence

   • Isolate compromised hosts (network-level segmentation), snapshot forensic evidence, and preserve logs. Don’t immediately wipe disks — capture images for later analysis. Use playbooks for common initial vectors (phish, web exploit, VPN compromise).

2. Remove persistent footholds

   • Hunt for and remove web shell implants, backdoors, new scheduled tasks/services, and changed configurations that enable reentry. Rotate credentials for accounts that could be compromised.

3. Assess scope and pivot points

   • Identify lateral movement attempts and adjacent systems the attacker could access. Short-term network segmentation can limit spread while you remediate.

4. Patch, rotate, and harden

   • Patch exploited vulnerabilities, update WAF rules, enforce stricter access controls for the affected systems, and apply any compensating controls identified in post-incident analysis.

5. Communicate & learn

   • Notify stakeholders, share IOC(s) with your threat intel team, update playbooks, and run a post-mortem to identify gaps (people/process/technology).
     

Practical checklist you can run through this week

• Inventory all public-facing apps and prioritize patches for high-risk CVEs.

• Enforce MFA on all remote access and cloud admin accounts.

• Turn off Autorun, require scanning of removable media, and log insertion events.

• Run phishing simulation + targeted user training, and enable attachment sandboxing.

• Add these three hunt queries (examples): suspicious web server POSTs to upload endpoints; new local admin creation outside change window; unusual successful VPN logins from rare geolocations.
  

Final notes

Initial Access tactics evolve — attackers innovate with fake CAPTCHAs, third-party service abuse, and supply-chain compromises — so prevention is about layers, detection is about telemetry and hunting, and response is about speed and playbooked actions. For the canonical technique list and sub-techniques, always consult the live MITRE ATT&CK pages and vendor guidance when writing controls or detection content.