Multi-factor authentication is one of the single most effective things a business can do to stop account takeovers – which is exactly why attackers have found a way to work around it that doesn’t involve breaking the technology at all. It just wears the person down instead.

How an MFA fatigue attack actually works

An attacker who already has a valid username and password (bought, phished, or reused from another breach) triggers the MFA push notification repeatedly – sometimes dozens of times in a row, often late at night. Most people reject the first few. Eventually, out of frustration, confusion, or the assumption it must be a glitch, someone taps “approve” just to make the notifications stop. That single tap hands the attacker in.

This isn’t a hypothetical: it’s the technique behind several high-profile breaches at large, security-conscious organisations in recent years, precisely because it targets human patience rather than a technical flaw.

Why standard push-based MFA is vulnerable

Simple approve/deny push notifications don’t require the user to prove they understand what they’re approving. They just require a tap. That’s convenient day-to-day, but it’s also the whole weakness attackers are exploiting.

What actually reduces the risk

• Number matching – requiring the user to type a code shown on the login screen into the authenticator app, rather than a single tap. This alone closes off most fatigue attacks.
• Rate limiting – capping how many MFA prompts an account can receive in a short window, and automatically flagging or locking accounts that exceed it.
• Phishing-resistant MFA – hardware security keys or passkeys (FIDO2) remove the “approve or deny” step entirely for the highest-risk accounts.
• Staff awareness – a five-minute briefing that an unexpected flood of MFA prompts should always be reported, never approved “to make it stop”, prevents most of these attacks outright.

If you’re on Microsoft 365 or Entra ID, number matching is something we can usually switch on with minimal disruption – it’s one of the highest-value, lowest-effort changes available right now.