The Anatomy of a Ransomware Attack: From Initial Access to Encryption

Ransomware attacks are not the instantaneous “everything encrypted at once” of the headlines. They are usually a staged process spanning days, sometimes weeks. Understanding these stages matters, because it is possible to detect and stop the attack before the encryption step. Here is the anatomy of a typical ransomware attack.

Stage 1: initial access

The attacker gets into the network somehow. The most common routes:

• Phishing: a user is tricked via a malicious attachment or link.
• Exposed external surface: an internet-facing service, weak/default-credential remote access (RDP, etc.), or an unpatched vulnerability.
• Leaked credentials: trying passwords leaked elsewhere (credential stuffing).

Initial access is why the security of your external surface matters so much; the attack’s door is usually here.

Stage 2: foothold and reconnaissance

After getting in, the attacker does not encrypt immediately. First they establish persistence, explore the network (which systems exist, where the data and backups are), and attempt privilege escalation.

Stage 3: lateral movement and backup destruction

With admin access, the attacker moves laterally, spreading to as many systems as possible. A critical and often-missed step: finding and deleting/encrypting the backups, to remove the victim’s recovery option and increase payment pressure. This is exactly why immutable/offline backups matter.

Stage 4: exfiltration and encryption

Modern ransomware often applies double extortion: first it exfiltrates the data, then encrypts it. So even if the victim does not pay, pressure continues with “we will publish the data.” Encryption is the final, most visible step — but by then the damage is done.

Defence at every stage

• Initial access: strong external surface, MFA, phishing awareness, patch management.
• Recon/spread: network segmentation, least privilege, anomaly detection.
• Backup destruction: immutable and offline backups.
• Exfiltration: outbound-data anomaly monitoring, data access controls.

Summary

Ransomware is a staged process: initial access → foothold/recon → lateral movement and backup destruction → exfiltration and encryption. Because encryption is the last step, the attack can be caught earlier. The most effective combination: a strong external surface (close the door), segmentation (slow the spread) and immutable backups (guarantee recovery).

Sources: CISA StopRansomware, MITRE ATT&CK.

Ransomware’s most common entry point is an exposed service or weak configuration on the external surface. CyberTestify’s scan maps that initial-access surface.