When OTP theft turns MFA into a weak link

OTP theft happens when someone manages to grab a one-time password before the legitimate user can use it. These codes are supposed to be short-lived and secure because they come through SMS, email, or an authenticator app, and they act as the “something you have” part of MFA. 

Attackers have learned how to intercept them through phishing pages, malware on mobile devices, or simple tricks that convince a user to repeat the code over the phone. Many OTP-based systems look solid on paper but turn out to be more fragile in the reality. In fact, one study, ‘Usable comprehensive-factor authentication for a secure time attendance system,’ puts the problem plainly: “In information security, it is widely accepted that the more authentication factors are used, the higher the security level. However, more factors cannot guarantee usability in real usage because human and other non-technical factors are involved.”

When delays or glitches occur during OTP delivery, something that happens often in e-health systems, attackers step into that timing gap and steal the code, giving them a path into protected accounts. Healthcare feels the impact sharply because so much depends on keeping EHRs and telehealth platforms locked down. MFA is supposed to give these systems a second line of defense, but once an attacker has both the password and the OTP, the entire setup collapses into single-factor security. 

If someone lifts an OTP or session cookie, they can slip into clinical dashboards or monitoring systems with almost no resistance. Some attacks even replay captured codes, bypassing biometric checks and hardware safeguards entirely.

The link between authentication, MFAs, and OTPs

Authentication is the basic gatekeeper that proves who or what is trying to access a system. It started with simple passwords and gradually expanded into MFA, which mixes different types of evidence, something you know, something you have, and something you are, to make attacks harder. 

In healthcare environments, especially the Internet of Healthcare Things (IoHT), this layering matters because the devices and networks often have tight resource limits and carry high-stakes data. OTPs sit at the heart of the “something you have” category; they’re short-lived codes sent by SMS, apps, or hardware tokens that confirm the user after the initial login. 

They’re meant to stop replay attempts by being unique for each session. Pairing OTPs with passwords gives clinics and telecare platforms a simple second barrier without adding too much overhead, though OTP systems depend on synchronized clocks and secure delivery channels, two things that don’t always behave predictably in the real world.

A Digital Health study on modern healthcare authentication captures the situation well, noting that “the concepts of MFA can be applied to healthcare where security can often be overlooked. The security requirements identified result in stronger methodologies of authentication such as hardware solutions in combination with biometric data to enhance MFA approaches. We identify the key vulnerabilities of weaker approaches to security such as password use against various cyber threats.”

How the duo OTP theft campaign works

Inital phase 

Attackers usually start a Duo OTP theft campaign by slipping phishing emails into inboxes from accounts they’ve already compromised inside the organization. Because these messages come from a familiar colleague or department, people lower their guard. The subjects rarely feel dramatic, things like payroll adjustments, health reminders, or staff recognition notices, just believable enough to prompt a quick click. 

The Digital Health study notes that “the concepts of MFA can be applied to healthcare where security can often be overlooked. The security requirements identified result in stronger methodologies of authentication such as hardware solutions in combination with biometric data to enhance MFA approaches. We identify the key vulnerabilities of weaker approaches to security such as password use against various cyber threats.”

The link leads to a fake login page that looks nearly identical to the real Duo-protected site. As one review on IoHT authentication notes, social-engineering succeeds when attackers exploit human factors in MFA, especially in environments like universities and hospitals, where overloaded staff trust internal senders. That familiarity is the weapon here, and attackers use it to scale their reach quickly, often with AI-generated email templates that sound convincingly routine.

The trap 

The trap relies on phishing kits that clone the real login experience down to the smallest detail. When victims land on these fake pages, JavaScript quietly scoops up their usernames and passwords and passes them to the attacker as URL parameters before moving them to what looks like a normal Duo OTP prompt. The whole setup feels legitimate because the branding, layout, and workflow are copied exactly. 

The study explains why this approach is so effective, noting that “authentication technologies are changing with the emerging field of cyber-related Internet of Things (IoT)… [but] information security can often be foreshadowed,” and attackers exploit those blind spots. OTP-based possession factors are especially exposed during these real-time interceptions because “MFA procedures can lead to human error and poor application of the policies in a workplace,” giving adversaries room to mimic trusted flows and harvest credentials without raising alarms. Once the victim enters their details, attackers exfiltrate everything through quiet AJAX POST requests and the trap closes cleanly.

MFA bypass 

The moment the victim enters the Duo OTP, the MFA bypass kicks in. The attacker captures the time-sensitive code instantly and uses it to log in as the victim in real time. To avoid suspicion, the phishing page hands the user off to the legitimate website, giving the impression that the login simply worked. 

The study’s authors describe the weakness clearly when they note that “multi-factor authentication (MFA) provides extra layers of security… [but] cyber attackers have relentlessly targeted the healthcare sector,” especially when MFA relies on OTPs without mutual authentication. In these cases, MFA collapses into little more than a dressed-up password because “weak password practices can be strengthened through MFA, but cyber-attacks can still take place even when using MFA.” Attackers simply move fast, exploiting OTPs’ extremely short lifespan and the absence of server-side verification to impersonate users instantly.

Post compromise events 

Once inside, attackers work quietly to secure persistence. They create mailbox rules that hide incoming alerts, forward sensitive information, and keep victims unaware. They often spread laterally by sending more phishing emails from the newly compromised account, using the same insider-trust advantage that opened the door in the first place. 

The study warns that these footholds are especially dangerous in healthcare, where “the interconnectedness of equipment and devices allows attackers to move through systems using compromised accounts because of shortcomings in authentication security.” That movement can expose PHI, enable ransomware deployment, and create systemic risk across IoHT networks. 

As the paper puts it, “cybercriminals put further stress on healthcare systems… causing public and private firms to become targets for further ransomware attacks that increase in complexity.” Attackers monetize the breach while avoiding detection for as long as possible.

Why healthcare organizations are especially vulnerable

Healthcare workers often need quick, remote access to electronic health records when they’re off-site or moving between departments, so OTPs sent by SMS or mobile apps have become the default security step. The problem is that this reliance on personal devices opens the door to familiar attacks like SIM swapping, smishing, or mobile malware, threats that fit easily into a clinical environment where staff use their phones constantly. 

Because OTPs are short-lived and travel over channels that aren’t always encrypted, they create openings an attacker can exploit. Even small oversights, like allowing repeated OTP attempts or using long timeout windows, give attackers enough room to guess or brute-force a code.

A Multidisciplinary Digital Publishing Institute (MDPI) study on out-of-hospital HIS access makes this risk clear, explaining that “in light of the need for Extramural Hospital Information System (HIS) access through mobile devices outside the hospital, this research analyzes situational information security threats, including the circumstances in which a mobile device may get lost and personal data may be stolen… the system needs to be implemented in accordance with the regulations,” and those threats directly apply to OTP delivery.

Human pressure adds another layer of risk. Healthcare settings run on tight schedules and high stress, and staff juggling multiple systems may not pause long enough to question an unexpected OTP prompt or a convincing phishing message. When someone is tired or rushing, it’s easy to hand over a code or miss the signs of a fake login request. At that point, MFA doesn’t act like a second barrier at all, it functions more like a single password with extra steps, and attackers know exactly how to take advantage of that.

See also: HIPAA Compliant Email: The Definitive Guide (2025 Update)

FAQs

Does HIPAA recommend any specific MFA type?

No. HIPAA is technology-neutral. 

When do healthcare organizations typically use MFA?

MFA is often deployed for systems that involve remote access, cloud services, administrative accounts, or applications containing electronic protected health information (ePHI).

Are SMS-based OTPs acceptable under HIPAA?

HIPAA does not prohibit SMS OTPs.