Credential Theft Emerges as the Most Damaging Driver of Healthcare Email Breaches
A new analysis of healthcare cybersecurity incidents shows that stolen login credentials were responsible for the most damaging email-related breaches in 2025, exposing more than 630,000 patient records—even though these incidents accounted for less than 20% of total reported email attacks. The findings highlight a growing imbalance between the frequency of certain cyberattacks and the scale of harm they cause, underscoring how a smaller subset of incidents can drive disproportionate risk across the healthcare sector.
The research, conducted by healthcare email security provider Paubox, reviewed breach reports submitted to the U.S. Department of Health and Human Services (HHS) throughout 2025. The company’s analysis identified three primary email-based attack patterns that together contributed to 170 breaches and impacted approximately 2.5 million individuals. Among these, phishing-driven mailbox takeovers stood out as the most destructive on a per-incident basis.
Mailbox Takeovers: Low Volume, High Impact
Mailbox takeover attacks—typically initiated through phishing emails—represented only about 17% of total healthcare email breaches reviewed in the study. However, the scale of exposure linked to these events far exceeded their share of incident counts. Once attackers successfully trick users into revealing credentials, they gain legitimate access to email accounts and can operate as if they were authorized employees.
This access enables threat actors to move quietly through inboxes and archives, often for extended periods. Instead of deploying ransomware or launching disruptive campaigns that trigger immediate alarms, attackers conducting mailbox takeovers frequently adopt a slower, stealthier approach. They search historical email threads, attachments, and stored communications for protected health information (PHI), financial data, and other sensitive records.
Because login activity appears valid on the surface—originating from real user accounts—traditional downstream security controls may fail to flag the compromise. Multi-factor authentication gaps, inconsistent monitoring of login behavior, and limited visibility into abnormal data access patterns all contribute to delayed detection.
According to the report, the root problem lies in a longstanding assumption embedded in many email security strategies: that users will successfully identify and avoid deception. Once that human layer fails and credentials are surrendered, many organizations lack sufficient safeguards to recognize that a trusted account has been hijacked.
Vendor and Business Associate Exposure Leads in Frequency
While mailbox takeovers caused the most damage per event, vendor and business associate email exposures were the most common breach pattern overall. These incidents accounted for nearly one-third of all email-related healthcare breaches analyzed.
Healthcare delivery is deeply interconnected with third-party service providers—billing companies, IT vendors, consultants, medical device suppliers, and cloud software platforms, among others. Each of these relationships involves the exchange of PHI and operational data through email and other communication tools.
When a vendor’s email environment is compromised, the impact can cascade across multiple healthcare organizations simultaneously. A single breach at a third-party provider may expose information belonging to numerous hospitals, clinics, or physician groups. This multi-tenant risk model makes vendor-related incidents particularly complex to manage and contain.
In many cases, healthcare organizations have limited visibility into the email security posture of their partners. Even when contracts include security clauses, practical enforcement and technical integration may lag behind. The result is an expanded attack surface that extends beyond the direct control of covered entities.
The study suggests that the scale of exposure in vendor-related email incidents often stems from centralized data handling practices. Vendors that aggregate information from multiple clients create high-value targets. Once attackers gain access, they can extract large volumes of PHI in a single campaign.
Impersonation Attacks Grow More Sophisticated
The third major pattern identified in the analysis involves executive and vendor impersonation. In these attacks, threat actors pose as trusted individuals—such as senior leaders, known suppliers, or internal staff members—to manipulate recipients into disclosing sensitive information.
Unlike traditional phishing that relies on generic lures, impersonation campaigns are increasingly targeted and context-aware. Attackers may study organizational structures, vendor relationships, and routine workflows to craft believable requests. Common scenarios include urgent payment instructions, document requests, or changes to vendor banking details.
Recent developments show that impersonation tactics are expanding beyond standard email spoofing. Threat actors are now abusing trusted platforms, including healthcare direct secure messaging systems and widely used cloud services, to deliver fraudulent messages. When communications arrive through channels that staff already view as legitimate and secure, skepticism naturally decreases.
This blending of trusted infrastructure with malicious intent makes detection significantly harder. Employees accustomed to acting quickly on routine vendor or executive communications may not pause to verify unusual requests, especially in high-pressure healthcare environments where speed is often critical.
The Financial Toll of Healthcare Breaches
The stakes for healthcare organizations remain exceptionally high. Industry data consistently shows that healthcare breaches carry the highest average cost compared to other sectors. Estimates place the average financial impact of a healthcare data breach at approximately $7.4 million per incident. Breaches involving third-party vendors also carry heavy consequences, with average costs nearing $4.9 million.
These figures reflect not only technical recovery expenses but also regulatory penalties, legal liabilities, operational disruptions, and reputational damage. For healthcare providers, the consequences extend further to patient trust, continuity of care, and potential risks to patient safety when systems or communications are compromised.
Why Healthcare Workflows Increase Risk
Healthcare operations present unique conditions that amplify email security risks. Clinical and administrative staff routinely handle urgent requests, time-sensitive communications, and frequent interactions with external partners. This environment creates fertile ground for social engineering.
An email requesting patient records, billing information, or vendor documentation may appear entirely routine. Attackers exploit this normalization of sensitive data exchange. When combined with heavy workloads and alert fatigue, the probability of a successful phishing or impersonation attempt increases.
Moreover, many healthcare organizations continue to rely heavily on email as a core communication channel, even as digital transformation expands the use of cloud platforms and remote access. This persistence ensures that email remains a central target for adversaries.
Shifting from Awareness to Prevention
The report emphasizes that user awareness training, while important, is insufficient as a standalone defense. As phishing tactics become more convincing and technologically advanced, the expectation that employees will consistently identify malicious messages is increasingly unrealistic.
Instead, the analysis argues for stronger controls at the email layer itself. Preventive technologies that detect and block phishing attempts, impersonation messages, and spoofed identities before they reach user inboxes are positioned as foundational safeguards. Once a malicious message lands in an inbox, the risk shifts heavily to human decision-making.
Additionally, organizations are encouraged to enhance monitoring of account behavior, enforce multi-factor authentication broadly, and adopt stricter controls around vendor access. Recognizing anomalous login patterns, unusual data access, or deviations from normal communication flows can help identify compromised accounts more quickly.
A Persistent Threat Landscape
The findings suggest that mailbox takeover will remain a persistent threat as long as phishing messages continue to reach users. Attackers need only a single successful credential harvest to gain extensive access. From there, the quiet, data-mining nature of these intrusions allows them to extract value while avoiding immediate detection.
In an ecosystem where healthcare data is highly valuable and widely distributed, email remains a primary gateway. The imbalance between incident frequency and impact—illustrated by credential theft’s outsized damage—signals that organizations must focus not only on how often attacks occur, but on which attack types carry the greatest potential harm.
As healthcare entities head into 2026, the message from this analysis is clear: defending email systems is no longer just about filtering spam or training users to spot suspicious links. It requires a layered, prevention-first approach that treats email as critical infrastructure—central to protecting patient information, maintaining trust, and ensuring operational resilience.
About Paubox
Paubox is a leader in HIPAA compliant email security for healthcare. Trusted by more than 8,000 organizations, including Cost Plus Drugs, Rippling, and Covenant Health, Paubox works with your existing platform to secure every email sent and received. Paubox is rated #1 on G2 and is recognized on G2’s 2025 Best Healthcare Software Products list. Paubox offers HIPAA compliant email encryption, AI-powered inbound email security, archiving, data loss prevention, a secure email API for transactional messaging, forms, and email marketing.
